Pleroma.Web.TwitterAPI.TwoFactorAuthenticationController -> Pleroma.Web.PleromaAPI.TwoFactorAuthenticationController

23 files changed, 1000 insertions, 9 deletions

diff --git a/lib/pleroma/mfa.ex b/lib/pleroma/mfa.ex
new file mode 100644
index 000000000..d353a4dad
--- /dev/null
+++ b/lib/pleroma/mfa.ex
@@ -0,0 +1,156 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.MFA do
+  @moduledoc """
+  The MFA context.
+  """
+
+  alias Comeonin.Pbkdf2
+  alias Pleroma.User
+
+  alias Pleroma.MFA.BackupCodes
+  alias Pleroma.MFA.Changeset
+  alias Pleroma.MFA.Settings
+  alias Pleroma.MFA.TOTP
+
+  @doc """
+  Returns MFA methods the user has enabled.
+
+  ## Examples
+
+    iex> Pleroma.MFA.supported_method(User)
+    "totp, u2f"
+  """
+  @spec supported_methods(User.t()) :: String.t()
+  def supported_methods(user) do
+    settings = fetch_settings(user)
+
+    Settings.mfa_methods()
+    |> Enum.reduce([], fn m, acc ->
+      if method_enabled?(m, settings) do
+        acc ++ [m]
+      else
+        acc
+      end
+    end)
+    |> Enum.join(",")
+  end
+
+  @doc "Checks that user enabled MFA"
+  def require?(user) do
+    fetch_settings(user).enabled
+  end
+
+  @doc """
+  Display MFA settings of user
+  """
+  def mfa_settings(user) do
+    settings = fetch_settings(user)
+
+    Settings.mfa_methods()
+    |> Enum.map(fn m -> [m, method_enabled?(m, settings)] end)
+    |> Enum.into(%{enabled: settings.enabled}, fn [a, b] -> {a, b} end)
+  end
+
+  @doc false
+  def fetch_settings(%User{} = user) do
+    user.multi_factor_authentication_settings || %Settings{}
+  end
+
+  @doc "clears backup codes"
+  def invalidate_backup_code(%User{} = user, hash_code) do
+    %{backup_codes: codes} = fetch_settings(user)
+
+    user
+    |> Changeset.cast_backup_codes(codes -- [hash_code])
+    |> User.update_and_set_cache()
+  end
+
+  @doc "generates backup codes"
+  @spec generate_backup_codes(User.t()) :: {:ok, list(binary)} | {:error, String.t()}
+  def generate_backup_codes(%User{} = user) do
+    with codes <- BackupCodes.generate(),
+         hashed_codes <- Enum.map(codes, &Pbkdf2.hashpwsalt/1),
+         changeset <- Changeset.cast_backup_codes(user, hashed_codes),
+         {:ok, _} <- User.update_and_set_cache(changeset) do
+      {:ok, codes}
+    else
+      {:error, msg} ->
+        %{error: msg}
+    end
+  end
+
+  @doc """
+  Generates secret key and set delivery_type to 'app' for TOTP method.
+  """
+  @spec setup_totp(User.t()) :: {:ok, User.t()} | {:error, Ecto.Changeset.t()}
+  def setup_totp(user) do
+    user
+    |> Changeset.setup_totp(%{secret: TOTP.generate_secret(), delivery_type: "app"})
+    |> User.update_and_set_cache()
+  end
+
+  @doc """
+  Confirms the TOTP method for user.
+
+  `attrs`:
+    `password` - current user password
+    `code` - TOTP token
+  """
+  @spec confirm_totp(User.t(), map()) :: {:ok, User.t()} | {:error, Ecto.Changeset.t() | atom()}
+  def confirm_totp(%User{} = user, attrs) do
+    with settings <- user.multi_factor_authentication_settings.totp,
+         {:ok, :pass} <- TOTP.validate_token(settings.secret, attrs["code"]) do
+      user
+      |> Changeset.confirm_totp()
+      |> User.update_and_set_cache()
+    end
+  end
+
+  @doc """
+  Disables the TOTP method for user.
+
+  `attrs`:
+    `password` - current user password
+  """
+  @spec disable_totp(User.t()) :: {:ok, User.t()} | {:error, Ecto.Changeset.t()}
+  def disable_totp(%User{} = user) do
+    user
+    |> Changeset.disable_totp()
+    |> Changeset.disable()
+    |> User.update_and_set_cache()
+  end
+
+  @doc """
+  Force disables all MFA methods for user.
+  """
+  @spec disable(User.t()) :: {:ok, User.t()} | {:error, Ecto.Changeset.t()}
+  def disable(%User{} = user) do
+    user
+    |> Changeset.disable_totp()
+    |> Changeset.disable(true)
+    |> User.update_and_set_cache()
+  end
+
+  @doc """
+  Checks if the user has MFA method enabled.
+  """
+  def method_enabled?(method, settings) do
+    with {:ok, %{confirmed: true} = _} <- Map.fetch(settings, method) do
+      true
+    else
+      _ -> false
+    end
+  end
+
+  @doc """
+  Checks if the user has enabled at least one MFA method.
+  """
+  def enabled?(settings) do
+    Settings.mfa_methods()
+    |> Enum.map(fn m -> method_enabled?(m, settings) end)
+    |> Enum.any?()
+  end
+end
diff --git a/lib/pleroma/mfa/backup_codes.ex b/lib/pleroma/mfa/backup_codes.ex
new file mode 100644
index 000000000..2b5ec34f8
--- /dev/null
+++ b/lib/pleroma/mfa/backup_codes.ex
@@ -0,0 +1,31 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.MFA.BackupCodes do
+  @moduledoc """
+  This module contains functions for generating backup codes.
+  """
+  alias Pleroma.Config
+
+  @config_ns [:instance, :multi_factor_authentication, :backup_codes]
+
+  @doc """
+  Generates backup codes.
+  """
+  @spec generate(Keyword.t()) :: list(String.t())
+  def generate(opts \\ []) do
+    number_of_codes = Keyword.get(opts, :number_of_codes, default_backup_codes_number())
+    code_length = Keyword.get(opts, :length, default_backup_codes_code_length())
+
+    Enum.map(1..number_of_codes, fn _ ->
+      :crypto.strong_rand_bytes(div(code_length, 2))
+      |> Base.encode16(case: :lower)
+    end)
+  end
+
+  defp default_backup_codes_number, do: Config.get(@config_ns ++ [:number], 5)
+
+  defp default_backup_codes_code_length,
+    do: Config.get(@config_ns ++ [:length], 16)
+end
diff --git a/lib/pleroma/mfa/changeset.ex b/lib/pleroma/mfa/changeset.ex
new file mode 100644
index 000000000..9b020aa8e
--- /dev/null
+++ b/lib/pleroma/mfa/changeset.ex
@@ -0,0 +1,64 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.MFA.Changeset do
+  alias Pleroma.MFA
+  alias Pleroma.MFA.Settings
+  alias Pleroma.User
+
+  def disable(%Ecto.Changeset{} = changeset, force \\ false) do
+    settings =
+      changeset
+      |> Ecto.Changeset.apply_changes()
+      |> MFA.fetch_settings()
+
+    if force || not MFA.enabled?(settings) do
+      put_change(changeset, %Settings{settings | enabled: false})
+    else
+      changeset
+    end
+  end
+
+  def disable_totp(%User{multi_factor_authentication_settings: settings} = user) do
+    user
+    |> put_change(%Settings{settings | totp: %Settings.TOTP{}})
+  end
+
+  def confirm_totp(%User{multi_factor_authentication_settings: settings} = user) do
+    totp_settings = %Settings.TOTP{settings.totp | confirmed: true}
+
+    user
+    |> put_change(%Settings{settings | totp: totp_settings, enabled: true})
+  end
+
+  def setup_totp(%User{} = user, attrs) do
+    mfa_settings = MFA.fetch_settings(user)
+
+    totp_settings =
+      %Settings.TOTP{}
+      |> Ecto.Changeset.cast(attrs, [:secret, :delivery_type])
+
+    user
+    |> put_change(%Settings{mfa_settings | totp: Ecto.Changeset.apply_changes(totp_settings)})
+  end
+
+  def cast_backup_codes(%User{} = user, codes) do
+    user
+    |> put_change(%Settings{
+      user.multi_factor_authentication_settings
+      | backup_codes: codes
+    })
+  end
+
+  defp put_change(%User{} = user, settings) do
+    user
+    |> Ecto.Changeset.change()
+    |> put_change(settings)
+  end
+
+  defp put_change(%Ecto.Changeset{} = changeset, settings) do
+    changeset
+    |> Ecto.Changeset.put_change(:multi_factor_authentication_settings, settings)
+  end
+end
diff --git a/lib/pleroma/mfa/settings.ex b/lib/pleroma/mfa/settings.ex
new file mode 100644
index 000000000..2764b889c
--- /dev/null
+++ b/lib/pleroma/mfa/settings.ex
@@ -0,0 +1,24 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.MFA.Settings do
+  use Ecto.Schema
+
+  @primary_key false
+
+  @mfa_methods [:totp]
+  embedded_schema do
+    field(:enabled, :boolean, default: false)
+    field(:backup_codes, {:array, :string}, default: [])
+
+    embeds_one :totp, TOTP, on_replace: :delete, primary_key: false do
+      field(:secret, :string)
+      # app | sms
+      field(:delivery_type, :string, default: "app")
+      field(:confirmed, :boolean, default: false)
+    end
+  end
+
+  def mfa_methods, do: @mfa_methods
+end
diff --git a/lib/pleroma/mfa/token.ex b/lib/pleroma/mfa/token.ex
new file mode 100644
index 000000000..25ff7fb29
--- /dev/null
+++ b/lib/pleroma/mfa/token.ex
@@ -0,0 +1,106 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.MFA.Token do
+  use Ecto.Schema
+  import Ecto.Query
+  import Ecto.Changeset
+
+  alias Pleroma.Repo
+  alias Pleroma.User
+  alias Pleroma.Web.OAuth.Authorization
+  alias Pleroma.Web.OAuth.Token, as: OAuthToken
+
+  @expires 300
+
+  schema "mfa_tokens" do
+    field(:token, :string)
+    field(:valid_until, :naive_datetime_usec)
+
+    belongs_to(:user, User, type: FlakeId.Ecto.CompatType)
+    belongs_to(:authorization, Authorization)
+
+    timestamps()
+  end
+
+  def get_by_token(token) do
+    from(
+      t in __MODULE__,
+      where: t.token == ^token,
+      preload: [:user, :authorization]
+    )
+    |> Repo.find_resource()
+  end
+
+  def validate(token) do
+    with {:fetch_token, {:ok, token}} <- {:fetch_token, get_by_token(token)},
+         {:expired, false} <- {:expired, is_expired?(token)} do
+      {:ok, token}
+    else
+      {:expired, _} -> {:error, :expired_token}
+      {:fetch_token, _} -> {:error, :not_found}
+      error -> {:error, error}
+    end
+  end
+
+  def create_token(%User{} = user) do
+    %__MODULE__{}
+    |> change
+    |> assign_user(user)
+    |> put_token
+    |> put_valid_until
+    |> Repo.insert()
+  end
+
+  def create_token(user, authorization) do
+    %__MODULE__{}
+    |> change
+    |> assign_user(user)
+    |> assign_authorization(authorization)
+    |> put_token
+    |> put_valid_until
+    |> Repo.insert()
+  end
+
+  defp assign_user(changeset, user) do
+    changeset
+    |> put_assoc(:user, user)
+    |> validate_required([:user])
+  end
+
+  defp assign_authorization(changeset, authorization) do
+    changeset
+    |> put_assoc(:authorization, authorization)
+    |> validate_required([:authorization])
+  end
+
+  defp put_token(changeset) do
+    changeset
+    |> change(%{token: OAuthToken.Utils.generate_token()})
+    |> validate_required([:token])
+    |> unique_constraint(:token)
+  end
+
+  defp put_valid_until(changeset) do
+    expires_in = NaiveDateTime.add(NaiveDateTime.utc_now(), @expires)
+
+    changeset
+    |> change(%{valid_until: expires_in})
+    |> validate_required([:valid_until])
+  end
+
+  def is_expired?(%__MODULE__{valid_until: valid_until}) do
+    NaiveDateTime.diff(NaiveDateTime.utc_now(), valid_until) > 0
+  end
+
+  def is_expired?(_), do: false
+
+  def delete_expired_tokens do
+    from(
+      q in __MODULE__,
+      where: fragment("?", q.valid_until) < ^Timex.now()
+    )
+    |> Repo.delete_all()
+  end
+end
diff --git a/lib/pleroma/mfa/totp.ex b/lib/pleroma/mfa/totp.ex
new file mode 100644
index 000000000..1407afc57
--- /dev/null
+++ b/lib/pleroma/mfa/totp.ex
@@ -0,0 +1,86 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.MFA.TOTP do
+  @moduledoc """
+  This module represents functions to create secrets for
+  TOTP Application as well as validate them with a time based token.
+  """
+  alias Pleroma.Config
+
+  @config_ns [:instance, :multi_factor_authentication, :totp]
+
+  @doc """
+  https://github.com/google/google-authenticator/wiki/Key-Uri-Format
+  """
+  def provisioning_uri(secret, label, opts \\ []) do
+    query =
+      %{
+        secret: secret,
+        issuer: Keyword.get(opts, :issuer, default_issuer()),
+        digits: Keyword.get(opts, :digits, default_digits()),
+        period: Keyword.get(opts, :period, default_period())
+      }
+      |> Enum.filter(fn {_, v} -> not is_nil(v) end)
+      |> Enum.into(%{})
+      |> URI.encode_query()
+
+    %URI{scheme: "otpauth", host: "totp", path: "/" <> label, query: query}
+    |> URI.to_string()
+  end
+
+  defp default_period, do: Config.get(@config_ns ++ [:period])
+  defp default_digits, do: Config.get(@config_ns ++ [:digits])
+
+  defp default_issuer,
+    do: Config.get(@config_ns ++ [:issuer], Config.get([:instance, :name]))
+
+  @doc "Creates a random Base 32 encoded string"
+  def generate_secret do
+    Base.encode32(:crypto.strong_rand_bytes(10))
+  end
+
+  @doc "Generates a valid token based on a secret"
+  def generate_token(secret) do
+    :pot.totp(secret)
+  end
+
+  @doc """
+  Validates a given token based on a secret.
+
+  optional parameters:
+  `token_length` default `6`
+  `interval_length` default `30`
+  `window` default 0
+
+  Returns {:ok, :pass} if the token is valid and
+  {:error, :invalid_token} if it is not.
+  """
+  @spec validate_token(String.t(), String.t()) ::
+          {:ok, :pass} | {:error, :invalid_token | :invalid_secret_and_token}
+  def validate_token(secret, token)
+      when is_binary(secret) and is_binary(token) do
+    opts = [
+      token_length: default_digits(),
+      interval_length: default_period()
+    ]
+
+    validate_token(secret, token, opts)
+  end
+
+  def validate_token(_, _), do: {:error, :invalid_secret_and_token}
+
+  @doc "See `validate_token/2`"
+  @spec validate_token(String.t(), String.t(), Keyword.t()) ::
+          {:ok, :pass} | {:error, :invalid_token | :invalid_secret_and_token}
+  def validate_token(secret, token, options)
+      when is_binary(secret) and is_binary(token) do
+    case :pot.valid_totp(token, secret, options) do
+      true -> {:ok, :pass}
+      false -> {:error, :invalid_token}
+    end
+  end
+
+  def validate_token(_, _, _), do: {:error, :invalid_secret_and_token}
+end
diff --git a/lib/pleroma/plugs/ensure_authenticated_plug.ex b/lib/pleroma/plugs/ensure_authenticated_plug.ex
index 9d5176e2b..3fe550806 100644
--- a/lib/pleroma/plugs/ensure_authenticated_plug.ex
+++ b/lib/pleroma/plugs/ensure_authenticated_plug.ex
@@ -15,6 +15,20 @@ defmodule Pleroma.Plugs.EnsureAuthenticatedPlug do
   end
 
   @impl true
+  def perform(
+        %{
+          assigns: %{
+            auth_credentials: %{password: _},
+            user: %User{multi_factor_authentication_settings: %{enabled: true}}
+          }
+        } = conn,
+        _
+      ) do
+    conn
+    |> render_error(:forbidden, "Two-factor authentication enabled, you must use a access token.")
+    |> halt()
+  end
+
   def perform(%{assigns: %{user: %User{}}} = conn, _) do
     conn
   end
diff --git a/lib/pleroma/user.ex b/lib/pleroma/user.ex
index 323eb2a41..a6f51f0be 100644
--- a/lib/pleroma/user.ex
+++ b/lib/pleroma/user.ex
@@ -20,6 +20,7 @@ defmodule Pleroma.User do
   alias Pleroma.Formatter
   alias Pleroma.HTML
   alias Pleroma.Keys
+  alias Pleroma.MFA
   alias Pleroma.Notification
   alias Pleroma.Object
   alias Pleroma.Registration
@@ -190,6 +191,12 @@ defmodule Pleroma.User do
     # `:subscribers` is deprecated (replaced with `subscriber_users` relation)
     field(:subscribers, {:array, :string}, default: [])
 
+    embeds_one(
+      :multi_factor_authentication_settings,
+      MFA.Settings,
+      on_replace: :delete
+    )
+
     timestamps()
   end
 
@@ -927,6 +934,7 @@ defmodule Pleroma.User do
     end
   end
 
+  @spec get_by_nickname(String.t()) :: User.t() | nil
   def get_by_nickname(nickname) do
     Repo.get_by(User, nickname: nickname) ||
       if Regex.match?(~r(@#{Pleroma.Web.Endpoint.host()})i, nickname) do
diff --git a/lib/pleroma/web/admin_api/admin_api_controller.ex b/lib/pleroma/web/admin_api/admin_api_controller.ex
index 80a4ebaac..9f1fd3aeb 100644
--- a/lib/pleroma/web/admin_api/admin_api_controller.ex
+++ b/lib/pleroma/web/admin_api/admin_api_controller.ex
@@ -10,6 +10,7 @@ defmodule Pleroma.Web.AdminAPI.AdminAPIController do
   alias Pleroma.Activity
   alias Pleroma.Config
   alias Pleroma.ConfigDB
+  alias Pleroma.MFA
   alias Pleroma.ModerationLog
   alias Pleroma.Plugs.OAuthScopesPlug
   alias Pleroma.ReportNote
@@ -61,6 +62,7 @@ defmodule Pleroma.Web.AdminAPI.AdminAPIController do
            :right_add,
            :right_add_multiple,
            :right_delete,
+           :disable_mfa,
            :right_delete_multiple,
            :update_user_credentials
          ]
@@ -674,6 +676,18 @@ defmodule Pleroma.Web.AdminAPI.AdminAPIController do
     json_response(conn, :no_content, "")
   end
 
+  @doc "Disable mfa for user's account."
+  def disable_mfa(conn, %{"nickname" => nickname}) do
+    case User.get_by_nickname(nickname) do
+      %User{} = user ->
+        MFA.disable(user)
+        json(conn, nickname)
+
+      _ ->
+        {:error, :not_found}
+    end
+  end
+
   @doc "Show a given user's credentials"
   def show_user_credentials(%{assigns: %{user: admin}} = conn, %{"nickname" => nickname}) do
     with %User{} = user <- User.get_cached_by_nickname_or_id(nickname) do
diff --git a/lib/pleroma/web/auth/pleroma_authenticator.ex b/lib/pleroma/web/auth/pleroma_authenticator.ex
index cb09664ce..a8f554aa3 100644
--- a/lib/pleroma/web/auth/pleroma_authenticator.ex
+++ b/lib/pleroma/web/auth/pleroma_authenticator.ex
@@ -19,8 +19,8 @@ defmodule Pleroma.Web.Auth.PleromaAuthenticator do
          {_, true} <- {:checkpw, AuthenticationPlug.checkpw(password, user.password_hash)} do
       {:ok, user}
     else
-      error ->
-        {:error, error}
+      {:error, _reason} = error -> error
+      error -> {:error, error}
     end
   end
 
diff --git a/lib/pleroma/web/auth/totp_authenticator.ex b/lib/pleroma/web/auth/totp_authenticator.ex
new file mode 100644
index 000000000..98aca9a51
--- /dev/null
+++ b/lib/pleroma/web/auth/totp_authenticator.ex
@@ -0,0 +1,45 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Auth.TOTPAuthenticator do
+  alias Comeonin.Pbkdf2
+  alias Pleroma.MFA
+  alias Pleroma.MFA.TOTP
+  alias Pleroma.User
+
+  @doc "Verify code or check backup code."
+  @spec verify(String.t(), User.t()) ::
+          {:ok, :pass} | {:error, :invalid_token | :invalid_secret_and_token}
+  def verify(
+        token,
+        %User{
+          multi_factor_authentication_settings:
+            %{enabled: true, totp: %{secret: secret, confirmed: true}} = _
+        } = _user
+      )
+      when is_binary(token) and byte_size(token) > 0 do
+    TOTP.validate_token(secret, token)
+  end
+
+  def verify(_, _), do: {:error, :invalid_token}
+
+  @spec verify_recovery_code(User.t(), String.t()) ::
+          {:ok, :pass} | {:error, :invalid_token}
+  def verify_recovery_code(
+        %User{multi_factor_authentication_settings: %{enabled: true, backup_codes: codes}} = user,
+        code
+      )
+      when is_list(codes) and is_binary(code) do
+    hash_code = Enum.find(codes, fn hash -> Pbkdf2.checkpw(code, hash) end)
+
+    if hash_code do
+      MFA.invalidate_backup_code(user, hash_code)
+      {:ok, :pass}
+    else
+      {:error, :invalid_token}
+    end
+  end
+
+  def verify_recovery_code(_, _), do: {:error, :invalid_token}
+end
diff --git a/lib/pleroma/web/common_api/utils.ex b/lib/pleroma/web/common_api/utils.ex
index 6540fa5d1..793f2e7f8 100644
--- a/lib/pleroma/web/common_api/utils.ex
+++ b/lib/pleroma/web/common_api/utils.ex
@@ -402,6 +402,7 @@ defmodule Pleroma.Web.CommonAPI.Utils do
     end
   end
 
+  @spec confirm_current_password(User.t(), String.t()) :: {:ok, User.t()} | {:error, String.t()}
   def confirm_current_password(user, password) do
     with %User{local: true} = db_user <- User.get_cached_by_id(user.id),
          true <- AuthenticationPlug.checkpw(password, db_user.password_hash) do
diff --git a/lib/pleroma/web/oauth/mfa_controller.ex b/lib/pleroma/web/oauth/mfa_controller.ex
new file mode 100644
index 000000000..e52cccd85
--- /dev/null
+++ b/lib/pleroma/web/oauth/mfa_controller.ex
@@ -0,0 +1,97 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.OAuth.MFAController do
+  @moduledoc """
+  The model represents api to use Multi Factor authentications.
+  """
+
+  use Pleroma.Web, :controller
+
+  alias Pleroma.MFA
+  alias Pleroma.Web.Auth.TOTPAuthenticator
+  alias Pleroma.Web.OAuth.MFAView, as: View
+  alias Pleroma.Web.OAuth.OAuthController
+  alias Pleroma.Web.OAuth.Token
+
+  plug(:fetch_session when action in [:show, :verify])
+  plug(:fetch_flash when action in [:show, :verify])
+
+  @doc """
+  Display form to input mfa code or recovery code.
+  """
+  def show(conn, %{"mfa_token" => mfa_token} = params) do
+    template = Map.get(params, "challenge_type", "totp")
+
+    conn
+    |> put_view(View)
+    |> render("#{template}.html", %{
+      mfa_token: mfa_token,
+      redirect_uri: params["redirect_uri"],
+      state: params["state"]
+    })
+  end
+
+  @doc """
+  Verification code and continue authorization.
+  """
+  def verify(conn, %{"mfa" => %{"mfa_token" => mfa_token} = mfa_params} = _) do
+    with {:ok, %{user: user, authorization: auth}} <- MFA.Token.validate(mfa_token),
+         {:ok, _} <- validates_challenge(user, mfa_params) do
+      conn
+      |> OAuthController.after_create_authorization(auth, %{
+        "authorization" => %{
+          "redirect_uri" => mfa_params["redirect_uri"],
+          "state" => mfa_params["state"]
+        }
+      })
+    else
+      _ ->
+        conn
+        |> put_flash(:error, "Two-factor authentication failed.")
+        |> put_status(:unauthorized)
+        |> show(mfa_params)
+    end
+  end
+
+  @doc """
+  Verification second step of MFA (or recovery) and returns access token.
+
+  ## Endpoint
+  POST /oauth/mfa/challenge
+
+  params:
+  `client_id`
+  `client_secret`
+  `mfa_token` - access token to check second step of mfa
+  `challenge_type` - 'totp' or 'recovery'
+  `code`
+
+  """
+  def challenge(conn, %{"mfa_token" => mfa_token} = params) do
+    with {:ok, app} <- Token.Utils.fetch_app(conn),
+         {:ok, %{user: user, authorization: auth}} <- MFA.Token.validate(mfa_token),
+         {:ok, _} <- validates_challenge(user, params),
+         {:ok, token} <- Token.exchange_token(app, auth) do
+      json(conn, Token.Response.build(user, token))
+    else
+      _error ->
+        conn
+        |> put_status(400)
+        |> json(%{error: "Invalid code"})
+    end
+  end
+
+  # Verify TOTP Code
+  defp validates_challenge(user, %{"challenge_type" => "totp", "code" => code} = _) do
+    TOTPAuthenticator.verify(code, user)
+  end
+
+  # Verify Recovery Code
+  defp validates_challenge(user, %{"challenge_type" => "recovery", "code" => code} = _) do
+    TOTPAuthenticator.verify_recovery_code(user, code)
+  end
+
+  defp validates_challenge(_, _), do: {:error, :unsupported_challenge_type}
+end
diff --git a/lib/pleroma/web/oauth/mfa_view.ex b/lib/pleroma/web/oauth/mfa_view.ex
new file mode 100644
index 000000000..e88e7066b
--- /dev/null
+++ b/lib/pleroma/web/oauth/mfa_view.ex
@@ -0,0 +1,8 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.OAuth.MFAView do
+  use Pleroma.Web, :view
+  import Phoenix.HTML.Form
+end
diff --git a/lib/pleroma/web/oauth/oauth_controller.ex b/lib/pleroma/web/oauth/oauth_controller.ex
index 685269877..7c804233c 100644
--- a/lib/pleroma/web/oauth/oauth_controller.ex
+++ b/lib/pleroma/web/oauth/oauth_controller.ex
@@ -6,6 +6,7 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   use Pleroma.Web, :controller
 
   alias Pleroma.Helpers.UriHelper
+  alias Pleroma.MFA
   alias Pleroma.Plugs.RateLimiter
   alias Pleroma.Registration
   alias Pleroma.Repo
@@ -14,6 +15,7 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   alias Pleroma.Web.ControllerHelper
   alias Pleroma.Web.OAuth.App
   alias Pleroma.Web.OAuth.Authorization
+  alias Pleroma.Web.OAuth.MFAController
   alias Pleroma.Web.OAuth.Scopes
   alias Pleroma.Web.OAuth.Token
   alias Pleroma.Web.OAuth.Token.Strategy.RefreshToken
@@ -121,7 +123,8 @@ defmodule Pleroma.Web.OAuth.OAuthController do
         %{"authorization" => _} = params,
         opts \\ []
       ) do
-    with {:ok, auth} <- do_create_authorization(conn, params, opts[:user]) do
+    with {:ok, auth, user} <- do_create_authorization(conn, params, opts[:user]),
+         {:mfa_required, _, _, false} <- {:mfa_required, user, auth, MFA.require?(user)} do
       after_create_authorization(conn, auth, params)
     else
       error ->
@@ -181,6 +184,22 @@ defmodule Pleroma.Web.OAuth.OAuthController do
 
   defp handle_create_authorization_error(
          %Plug.Conn{} = conn,
+         {:mfa_required, user, auth, _},
+         params
+       ) do
+    {:ok, token} = MFA.Token.create_token(user, auth)
+
+    data = %{
+      "mfa_token" => token.token,
+      "redirect_uri" => params["authorization"]["redirect_uri"],
+      "state" => params["authorization"]["state"]
+    }
+
+    MFAController.show(conn, data)
+  end
+
+  defp handle_create_authorization_error(
+         %Plug.Conn{} = conn,
          {:account_status, :password_reset_pending},
          %{"authorization" => _} = params
        ) do
@@ -231,7 +250,8 @@ defmodule Pleroma.Web.OAuth.OAuthController do
 
       json(conn, Token.Response.build(user, token, response_attrs))
     else
-      _error -> render_invalid_credentials_error(conn)
+      error ->
+        handle_token_exchange_error(conn, error)
     end
   end
 
@@ -244,6 +264,7 @@ defmodule Pleroma.Web.OAuth.OAuthController do
          {:account_status, :active} <- {:account_status, User.account_status(user)},
          {:ok, scopes} <- validate_scopes(app, params),
          {:ok, auth} <- Authorization.create_authorization(app, user, scopes),
+         {:mfa_required, _, _, false} <- {:mfa_required, user, auth, MFA.require?(user)},
          {:ok, token} <- Token.exchange_token(app, auth) do
       json(conn, Token.Response.build(user, token))
     else
@@ -270,13 +291,20 @@ defmodule Pleroma.Web.OAuth.OAuthController do
          {:ok, token} <- Token.exchange_token(app, auth) do
       json(conn, Token.Response.build_for_client_credentials(token))
     else
-      _error -> render_invalid_credentials_error(conn)
+      _error ->
+        handle_token_exchange_error(conn, :invalid_credentails)
     end
   end
 
   # Bad request
   def token_exchange(%Plug.Conn{} = conn, params), do: bad_request(conn, params)
 
+  defp handle_token_exchange_error(%Plug.Conn{} = conn, {:mfa_required, user, auth, _}) do
+    conn
+    |> put_status(:forbidden)
+    |> json(build_and_response_mfa_token(user, auth))
+  end
+
   defp handle_token_exchange_error(%Plug.Conn{} = conn, {:account_status, :deactivated}) do
     render_error(
       conn,
@@ -434,7 +462,8 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   def register(%Plug.Conn{} = conn, %{"authorization" => _, "op" => "connect"} = params) do
     with registration_id when not is_nil(registration_id) <- get_session_registration_id(conn),
          %Registration{} = registration <- Repo.get(Registration, registration_id),
-         {_, {:ok, auth}} <- {:create_authorization, do_create_authorization(conn, params)},
+         {_, {:ok, auth, _user}} <-
+           {:create_authorization, do_create_authorization(conn, params)},
          %User{} = user <- Repo.preload(auth, :user).user,
          {:ok, _updated_registration} <- Registration.bind_to_user(registration, user) do
       conn
@@ -500,8 +529,9 @@ defmodule Pleroma.Web.OAuth.OAuthController do
          %App{} = app <- Repo.get_by(App, client_id: client_id),
          true <- redirect_uri in String.split(app.redirect_uris),
          {:ok, scopes} <- validate_scopes(app, auth_attrs),
-         {:account_status, :active} <- {:account_status, User.account_status(user)} do
-      Authorization.create_authorization(app, user, scopes)
+         {:account_status, :active} <- {:account_status, User.account_status(user)},
+         {:ok, auth} <- Authorization.create_authorization(app, user, scopes) do
+      {:ok, auth, user}
     end
   end
 
@@ -515,6 +545,12 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   defp put_session_registration_id(%Plug.Conn{} = conn, registration_id),
     do: put_session(conn, :registration_id, registration_id)
 
+  defp build_and_response_mfa_token(user, auth) do
+    with {:ok, token} <- MFA.Token.create_token(user, auth) do
+      Token.Response.build_for_mfa_token(user, token)
+    end
+  end
+
   @spec validate_scopes(App.t(), map()) ::
           {:ok, list()} | {:error, :missing_scopes | :unsupported_scopes}
   defp validate_scopes(%App{} = app, params) do
diff --git a/lib/pleroma/web/oauth/token/clean_worker.ex b/lib/pleroma/web/oauth/token/clean_worker.ex
new file mode 100644
index 000000000..2c3bb9ded
--- /dev/null
+++ b/lib/pleroma/web/oauth/token/clean_worker.ex
@@ -0,0 +1,38 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.OAuth.Token.CleanWorker do
+  @moduledoc """
+  The module represents functions to clean an expired OAuth and MFA tokens.
+  """
+  use GenServer
+
+  @ten_seconds 10_000
+  @one_day 86_400_000
+
+  alias Pleroma.MFA
+  alias Pleroma.Web.OAuth
+  alias Pleroma.Workers.BackgroundWorker
+
+  def start_link(_), do: GenServer.start_link(__MODULE__, %{})
+
+  def init(_) do
+    Process.send_after(self(), :perform, @ten_seconds)
+    {:ok, nil}
+  end
+
+  @doc false
+  def handle_info(:perform, state) do
+    BackgroundWorker.enqueue("clean_expired_tokens", %{})
+    interval = Pleroma.Config.get([:oauth2, :clean_expired_tokens_interval], @one_day)
+
+    Process.send_after(self(), :perform, interval)
+    {:noreply, state}
+  end
+
+  def perform(:clean) do
+    OAuth.Token.delete_expired_tokens()
+    MFA.Token.delete_expired_tokens()
+  end
+end
diff --git a/lib/pleroma/web/oauth/token/response.ex b/lib/pleroma/web/oauth/token/response.ex
index 6f4713dee..0e72c31e9 100644
--- a/lib/pleroma/web/oauth/token/response.ex
+++ b/lib/pleroma/web/oauth/token/response.ex
@@ -5,6 +5,7 @@
 defmodule Pleroma.Web.OAuth.Token.Response do
   @moduledoc false
 
+  alias Pleroma.MFA
   alias Pleroma.User
   alias Pleroma.Web.OAuth.Token.Utils
 
@@ -32,5 +33,13 @@ defmodule Pleroma.Web.OAuth.Token.Response do
     }
   end
 
+  def build_for_mfa_token(user, mfa_token) do
+    %{
+      error: "mfa_required",
+      mfa_token: mfa_token.token,
+      supported_challenge_types: MFA.supported_methods(user)
+    }
+  end
+
   defp expires_in, do: Pleroma.Config.get([:oauth2, :token_expires_in], 600)
 end
diff --git a/lib/pleroma/web/pleroma_api/controllers/two_factor_authentication_controller.ex b/lib/pleroma/web/pleroma_api/controllers/two_factor_authentication_controller.ex
new file mode 100644
index 000000000..eb9989cdf
--- /dev/null
+++ b/lib/pleroma/web/pleroma_api/controllers/two_factor_authentication_controller.ex
@@ -0,0 +1,133 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.PleromaAPI.TwoFactorAuthenticationController do
+  @moduledoc "The module represents actions to manage MFA"
+  use Pleroma.Web, :controller
+
+  import Pleroma.Web.ControllerHelper, only: [json_response: 3]
+
+  alias Pleroma.MFA
+  alias Pleroma.MFA.TOTP
+  alias Pleroma.Plugs.OAuthScopesPlug
+  alias Pleroma.Web.CommonAPI.Utils
+
+  plug(OAuthScopesPlug, %{scopes: ["read:security"]} when action in [:settings])
+
+  plug(
+    OAuthScopesPlug,
+    %{scopes: ["write:security"]} when action in [:setup, :confirm, :disable, :backup_codes]
+  )
+
+  @doc """
+  Gets user multi factor authentication settings
+
+  ## Endpoint
+  GET /api/pleroma/accounts/mfa
+
+  """
+  def settings(%{assigns: %{user: user}} = conn, _params) do
+    json(conn, %{settings: MFA.mfa_settings(user)})
+  end
+
+  @doc """
+  Prepare setup mfa method
+
+  ## Endpoint
+  GET /api/pleroma/accounts/mfa/setup/[:method]
+
+  """
+  def setup(%{assigns: %{user: user}} = conn, %{"method" => "totp"} = _params) do
+    with {:ok, user} <- MFA.setup_totp(user),
+         %{secret: secret} = _ <- user.multi_factor_authentication_settings.totp do
+      provisioning_uri = TOTP.provisioning_uri(secret, "#{user.email}")
+
+      json(conn, %{provisioning_uri: provisioning_uri, key: secret})
+    else
+      {:error, message} ->
+        json_response(conn, :unprocessable_entity, %{error: message})
+    end
+  end
+
+  def setup(conn, _params) do
+    json_response(conn, :bad_request, %{error: "undefined method"})
+  end
+
+  @doc """
+  Confirms setup and enable mfa method
+
+  ## Endpoint
+  POST /api/pleroma/accounts/mfa/confirm/:method
+
+  - params:
+  `code` - confirmation code
+  `password` - current password
+  """
+  def confirm(
+        %{assigns: %{user: user}} = conn,
+        %{"method" => "totp", "password" => _, "code" => _} = params
+      ) do
+    with {:ok, _user} <- Utils.confirm_current_password(user, params["password"]),
+         {:ok, _user} <- MFA.confirm_totp(user, params) do
+      json(conn, %{})
+    else
+      {:error, message} ->
+        json_response(conn, :unprocessable_entity, %{error: message})
+    end
+  end
+
+  def confirm(conn, _) do
+    json_response(conn, :bad_request, %{error: "undefined mfa method"})
+  end
+
+  @doc """
+  Disable mfa method and disable mfa if need.
+  """
+  def disable(%{assigns: %{user: user}} = conn, %{"method" => "totp"} = params) do
+    with {:ok, user} <- Utils.confirm_current_password(user, params["password"]),
+         {:ok, _user} <- MFA.disable_totp(user) do
+      json(conn, %{})
+    else
+      {:error, message} ->
+        json_response(conn, :unprocessable_entity, %{error: message})
+    end
+  end
+
+  def disable(%{assigns: %{user: user}} = conn, %{"method" => "mfa"} = params) do
+    with {:ok, user} <- Utils.confirm_current_password(user, params["password"]),
+         {:ok, _user} <- MFA.disable(user) do
+      json(conn, %{})
+    else
+      {:error, message} ->
+        json_response(conn, :unprocessable_entity, %{error: message})
+    end
+  end
+
+  def disable(conn, _) do
+    json_response(conn, :bad_request, %{error: "undefined mfa method"})
+  end
+
+  @doc """
+  Generates backup codes.
+
+  ## Endpoint
+  GET /api/pleroma/accounts/mfa/backup_codes
+
+  ## Response
+  ### Success
+  `{codes: [codes]}`
+
+  ### Error
+  `{error: [error_message]}`
+
+  """
+  def backup_codes(%{assigns: %{user: user}} = conn, _params) do
+    with {:ok, codes} <- MFA.generate_backup_codes(user) do
+      json(conn, %{codes: codes})
+    else
+      {:error, message} ->
+        json_response(conn, :unprocessable_entity, %{error: message})
+    end
+  end
+end
diff --git a/lib/pleroma/web/router.ex b/lib/pleroma/web/router.ex
index 281516bb8..7a171f9fb 100644
--- a/lib/pleroma/web/router.ex
+++ b/lib/pleroma/web/router.ex
@@ -132,6 +132,7 @@ defmodule Pleroma.Web.Router do
     post("/users/follow", AdminAPIController, :user_follow)
     post("/users/unfollow", AdminAPIController, :user_unfollow)
 
+    put("/users/disable_mfa", AdminAPIController, :disable_mfa)
     delete("/users", AdminAPIController, :user_delete)
     post("/users", AdminAPIController, :users_create)
     patch("/users/:nickname/toggle_activation", AdminAPIController, :user_toggle_activation)
@@ -258,6 +259,16 @@ defmodule Pleroma.Web.Router do
     post("/follow_import", UtilController, :follow_import)
   end
 
+  scope "/api/pleroma", Pleroma.Web.PleromaAPI do
+    pipe_through(:authenticated_api)
+
+    get("/accounts/mfa", TwoFactorAuthenticationController, :settings)
+    get("/accounts/mfa/backup_codes", TwoFactorAuthenticationController, :backup_codes)
+    get("/accounts/mfa/setup/:method", TwoFactorAuthenticationController, :setup)
+    post("/accounts/mfa/confirm/:method", TwoFactorAuthenticationController, :confirm)
+    delete("/accounts/mfa/:method", TwoFactorAuthenticationController, :disable)
+  end
+
   scope "/oauth", Pleroma.Web.OAuth do
     scope [] do
       pipe_through(:oauth)
@@ -269,6 +280,10 @@ defmodule Pleroma.Web.Router do
     post("/revoke", OAuthController, :token_revoke)
     get("/registration_details", OAuthController, :registration_details)
 
+    post("/mfa/challenge", MFAController, :challenge)
+    post("/mfa/verify", MFAController, :verify, as: :mfa_verify)
+    get("/mfa", MFAController, :show)
+
     scope [] do
       pipe_through(:browser)
 
diff --git a/lib/pleroma/web/templates/o_auth/mfa/recovery.html.eex b/lib/pleroma/web/templates/o_auth/mfa/recovery.html.eex
new file mode 100644
index 000000000..750f65386
--- /dev/null
+++ b/lib/pleroma/web/templates/o_auth/mfa/recovery.html.eex
@@ -0,0 +1,24 @@
+<%= if get_flash(@conn, :info) do %>
+<p class="alert alert-info" role="alert"><%= get_flash(@conn, :info) %></p>
+<% end %>
+<%= if get_flash(@conn, :error) do %>
+<p class="alert alert-danger" role="alert"><%= get_flash(@conn, :error) %></p>
+<% end %>
+
+<h2>Two-factor recovery</h2>
+
+<%= form_for @conn, mfa_verify_path(@conn, :verify), [as: "mfa"], fn f -> %>
+<div class="input">
+  <%= label f, :code, "Recovery code" %>
+  <%= text_input f, :code %>
+  <%= hidden_input f, :mfa_token, value: @mfa_token %>
+  <%= hidden_input f, :state, value: @state %>
+  <%= hidden_input f, :redirect_uri, value: @redirect_uri %>
+  <%= hidden_input f, :challenge_type, value: "recovery" %>
+</div>
+
+<%= submit "Verify" %>
+<% end %>
+<a href="<%= mfa_path(@conn, :show, %{challenge_type: "totp", mfa_token: @mfa_token, state: @state, redirect_uri: @redirect_uri}) %>">
+  Enter a two-factor code
+</a>
diff --git a/lib/pleroma/web/templates/o_auth/mfa/totp.html.eex b/lib/pleroma/web/templates/o_auth/mfa/totp.html.eex
new file mode 100644
index 000000000..af6e546b0
--- /dev/null
+++ b/lib/pleroma/web/templates/o_auth/mfa/totp.html.eex
@@ -0,0 +1,24 @@
+<%= if get_flash(@conn, :info) do %>
+<p class="alert alert-info" role="alert"><%= get_flash(@conn, :info) %></p>
+<% end %>
+<%= if get_flash(@conn, :error) do %>
+<p class="alert alert-danger" role="alert"><%= get_flash(@conn, :error) %></p>
+<% end %>
+
+<h2>Two-factor authentication</h2>
+
+<%= form_for @conn, mfa_verify_path(@conn, :verify), [as: "mfa"], fn f -> %>
+<div class="input">
+  <%= label f, :code, "Authentication code" %>
+  <%= text_input f, :code %>
+  <%= hidden_input f, :mfa_token, value: @mfa_token %>
+  <%= hidden_input f, :state, value: @state %>
+  <%= hidden_input f, :redirect_uri, value: @redirect_uri %>
+  <%= hidden_input f, :challenge_type, value: "totp" %>
+</div>
+
+<%= submit "Verify" %>
+<% end %>
+<a href="<%= mfa_path(@conn, :show, %{challenge_type: "recovery", mfa_token: @mfa_token, state: @state, redirect_uri: @redirect_uri}) %>">
+  Enter a two-factor recovery code
+</a>
diff --git a/lib/pleroma/web/templates/twitter_api/remote_follow/follow_mfa.html.eex b/lib/pleroma/web/templates/twitter_api/remote_follow/follow_mfa.html.eex
new file mode 100644
index 000000000..adc3a3e3d
--- /dev/null
+++ b/lib/pleroma/web/templates/twitter_api/remote_follow/follow_mfa.html.eex
@@ -0,0 +1,13 @@
+<%= if @error do %>
+<h2><%= @error %></h2>
+<% end %>
+<h2>Two-factor authentication</h2>
+<p><%= @followee.nickname %></p>
+<img height="128" width="128" src="<%= avatar_url(@followee) %>">
+<%= form_for @conn, remote_follow_path(@conn, :do_follow), [as: "mfa"], fn f -> %>
+<%= text_input f, :code, placeholder: "Authentication code", required: true %>
+<br>
+<%= hidden_input f, :id, value: @followee.id %>
+<%= hidden_input f, :token, value: @mfa_token %>
+<%= submit "Authorize" %>
+<% end %>
diff --git a/lib/pleroma/web/twitter_api/controllers/remote_follow_controller.ex b/lib/pleroma/web/twitter_api/controllers/remote_follow_controller.ex
index 89da760da..521dc9322 100644
--- a/lib/pleroma/web/twitter_api/controllers/remote_follow_controller.ex
+++ b/lib/pleroma/web/twitter_api/controllers/remote_follow_controller.ex
@@ -8,10 +8,12 @@ defmodule Pleroma.Web.TwitterAPI.RemoteFollowController do
   require Logger
 
   alias Pleroma.Activity
+  alias Pleroma.MFA
   alias Pleroma.Object.Fetcher
   alias Pleroma.Plugs.OAuthScopesPlug
   alias Pleroma.User
   alias Pleroma.Web.Auth.Authenticator
+  alias Pleroma.Web.Auth.TOTPAuthenticator
   alias Pleroma.Web.CommonAPI
 
   @status_types ["Article", "Event", "Note", "Video", "Page", "Question"]
@@ -68,6 +70,8 @@ defmodule Pleroma.Web.TwitterAPI.RemoteFollowController do
 
   # POST  /ostatus_subscribe
   #
+  # adds a remote account in followers if user already is signed in.
+  #
   def do_follow(%{assigns: %{user: %User{} = user}} = conn, %{"user" => %{"id" => id}}) do
     with {:fetch_user, %User{} = followee} <- {:fetch_user, User.get_cached_by_id(id)},
          {:ok, _, _, _} <- CommonAPI.follow(user, followee) do
@@ -78,9 +82,33 @@ defmodule Pleroma.Web.TwitterAPI.RemoteFollowController do
     end
   end
 
+  # POST  /ostatus_subscribe
+  #
+  # step 1.
+  # checks login\password and displays step 2 form of MFA if need.
+  #
   def do_follow(conn, %{"authorization" => %{"name" => _, "password" => _, "id" => id}}) do
-    with {:fetch_user, %User{} = followee} <- {:fetch_user, User.get_cached_by_id(id)},
+    with {_, %User{} = followee} <- {:fetch_user, User.get_cached_by_id(id)},
          {_, {:ok, user}, _} <- {:auth, Authenticator.get_user(conn), followee},
+         {_, _, _, false} <- {:mfa_required, followee, user, MFA.require?(user)},
+         {:ok, _, _, _} <- CommonAPI.follow(user, followee) do
+      redirect(conn, to: "/users/#{followee.id}")
+    else
+      error ->
+        handle_follow_error(conn, error)
+    end
+  end
+
+  # POST  /ostatus_subscribe
+  #
+  # step 2
+  # checks TOTP code. otherwise displays form with errors
+  #
+  def do_follow(conn, %{"mfa" => %{"code" => code, "token" => token, "id" => id}}) do
+    with {_, %User{} = followee} <- {:fetch_user, User.get_cached_by_id(id)},
+         {_, _, {:ok, %{user: user}}} <- {:mfa_token, followee, MFA.Token.validate(token)},
+         {_, _, _, {:ok, _}} <-
+           {:verify_mfa_code, followee, token, TOTPAuthenticator.verify(code, user)},
          {:ok, _, _, _} <- CommonAPI.follow(user, followee) do
       redirect(conn, to: "/users/#{followee.id}")
     else
@@ -94,6 +122,23 @@ defmodule Pleroma.Web.TwitterAPI.RemoteFollowController do
     render(conn, "followed.html", %{error: "Insufficient permissions: follow | write:follows."})
   end
 
+  defp handle_follow_error(conn, {:mfa_token, followee, _} = _) do
+    render(conn, "follow_login.html", %{error: "Wrong username or password", followee: followee})
+  end
+
+  defp handle_follow_error(conn, {:verify_mfa_code, followee, token, _} = _) do
+    render(conn, "follow_mfa.html", %{
+      error: "Wrong authentication code",
+      followee: followee,
+      mfa_token: token
+    })
+  end
+
+  defp handle_follow_error(conn, {:mfa_required, followee, user, _} = _) do
+    {:ok, %{token: token}} = MFA.Token.create_token(user)
+    render(conn, "follow_mfa.html", %{followee: followee, mfa_token: token, error: false})
+  end
+
   defp handle_follow_error(conn, {:auth, _, followee} = _) do
     render(conn, "follow_login.html", %{error: "Wrong username or password", followee: followee})
   end