Authentication Plug: Update bcrypt password on login.

lib/pleroma/plugs/authentication_plug.ex

@@ -30,6 +30,17 @@ defmodule Pleroma.Plugs.AuthenticationPlug do
     false
   end
 
+  def maybe_update_password(%User{password_hash: "$2" <> _} = user, password) do
+    user
+    |> User.password_update_changeset(%{
+      "password" => password,
+      "password_confirmation" => password
+    })
+    |> Pleroma.Repo.update()
+  end
+
+  def maybe_update_password(user, _), do: {:ok, user}
+
   def call(%{assigns: %{user: %User{}}} = conn, _), do: conn
 
   def call(
@@ -42,6 +53,8 @@ defmodule Pleroma.Plugs.AuthenticationPlug do
         _
       ) do
     if checkpw(password, password_hash) do
+      {:ok, auth_user} = maybe_update_password(auth_user, password)
+
       conn
       |> assign(:user, auth_user)
       |> OAuthScopesPlug.skip_plug()