diff --git a/config/config.exs b/config/config.exs
index 326c4b601..ccdd35777 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -370,6 +370,17 @@ config :auto_linker,
     rel: false
   ]
 
+config :pleroma, :ldap,
+  enabled: System.get_env("LDAP_ENABLED") == "true",
+  host: System.get_env("LDAP_HOST") || "localhost",
+  port: String.to_integer(System.get_env("LDAP_PORT") || "389"),
+  ssl: System.get_env("LDAP_SSL") == "true",
+  sslopts: [],
+  tls: System.get_env("LDAP_TLS") == "true",
+  tlsopts: [],
+  base: System.get_env("LDAP_BASE") || "dc=example,dc=com",
+  uid: System.get_env("LDAP_UID") || "cn"
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{Mix.env()}.exs"
diff --git a/docs/config.md b/docs/config.md
index e34ffe980..201180373 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -331,3 +331,26 @@ config :auto_linker,
     rel: false
   ]
 ```
+
+## :ldap
+
+Use LDAP for user authentication.  When a user logs in to the Pleroma
+instance, the name and password will be verified by trying to authenticate
+(bind) to an LDAP server.  If a user exists in the LDAP directory but there
+is no account with the same name yet on the Pleroma instance then a new
+Pleroma account will be created with the same name as the LDAP user name.
+
+* `enabled`: enables LDAP authentication
+* `host`: LDAP server hostname
+* `port`: LDAP port, e.g. 389 or 636
+* `ssl`: true to use SSL, usually implies the port 636
+* `sslopts`: additional SSL options
+* `tls`: true to start TLS, usually implies the port 389
+* `tlsopts`: additional TLS options
+* `base`: LDAP base, e.g. "dc=example,dc=com"
+* `uid`: LDAP attribute name to authenticate the user, e.g. when "cn", the filter will be "cn=username,base"
+
+## Pleroma.Web.Auth.Authenticator
+
+* `Pleroma.Web.Auth.PleromaAuthenticator`: default database authenticator
+* `Pleroma.Web.Auth.LDAPAuthenticator`: LDAP authentication
diff --git a/lib/pleroma/web/auth/ldap_authenticator.ex b/lib/pleroma/web/auth/ldap_authenticator.ex
new file mode 100644
index 000000000..88217aab8
--- /dev/null
+++ b/lib/pleroma/web/auth/ldap_authenticator.ex
@@ -0,0 +1,143 @@
+# 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.LDAPAuthenticator do
+  alias Pleroma.User
+
+  require Logger
+
+  @behaviour Pleroma.Web.Auth.Authenticator
+
+  @connection_timeout 10_000
+  @search_timeout 10_000
+
+  def get_user(%Plug.Conn{} = conn) do
+    if Pleroma.Config.get([:ldap, :enabled]) do
+      {name, password} =
+        case conn.params do
+          %{"authorization" => %{"name" => name, "password" => password}} ->
+            {name, password}
+
+          %{"grant_type" => "password", "username" => name, "password" => password} ->
+            {name, password}
+        end
+
+      case ldap_user(name, password) do
+        %User{} = user ->
+          {:ok, user}
+
+        {:error, {:ldap_connection_error, _}} ->
+          # When LDAP is unavailable, try default authenticator
+          Pleroma.Web.Auth.PleromaAuthenticator.get_user(conn)
+
+        error ->
+          error
+      end
+    else
+      # Fall back to default authenticator
+      Pleroma.Web.Auth.PleromaAuthenticator.get_user(conn)
+    end
+  end
+
+  def handle_error(%Plug.Conn{} = _conn, error) do
+    error
+  end
+
+  def auth_template, do: nil
+
+  defp ldap_user(name, password) do
+    ldap = Pleroma.Config.get(:ldap, [])
+    host = Keyword.get(ldap, :host, "localhost")
+    port = Keyword.get(ldap, :port, 389)
+    ssl = Keyword.get(ldap, :ssl, false)
+    sslopts = Keyword.get(ldap, :sslopts, [])
+
+    options =
+      [{:port, port}, {:ssl, ssl}, {:timeout, @connection_timeout}] ++
+        if sslopts != [], do: [{:sslopts, sslopts}], else: []
+
+    case :eldap.open([to_charlist(host)], options) do
+      {:ok, connection} ->
+        try do
+          if Keyword.get(ldap, :tls, false) do
+            :application.ensure_all_started(:ssl)
+
+            case :eldap.start_tls(
+                   connection,
+                   Keyword.get(ldap, :tlsopts, []),
+                   @connection_timeout
+                 ) do
+              :ok ->
+                :ok
+
+              error ->
+                Logger.error("Could not start TLS: #{inspect(error)}")
+            end
+          end
+
+          bind_user(connection, ldap, name, password)
+        after
+          :eldap.close(connection)
+        end
+
+      {:error, error} ->
+        Logger.error("Could not open LDAP connection: #{inspect(error)}")
+        {:error, {:ldap_connection_error, error}}
+    end
+  end
+
+  defp bind_user(connection, ldap, name, password) do
+    uid = Keyword.get(ldap, :uid, "cn")
+    base = Keyword.get(ldap, :base)
+
+    case :eldap.simple_bind(connection, "#{uid}=#{name},#{base}", password) do
+      :ok ->
+        case User.get_by_nickname_or_email(name) do
+          %User{} = user ->
+            user
+
+          _ ->
+            register_user(connection, base, uid, name, password)
+        end
+
+      error ->
+        error
+    end
+  end
+
+  defp register_user(connection, base, uid, name, password) do
+    case :eldap.search(connection, [
+           {:base, to_charlist(base)},
+           {:filter, :eldap.equalityMatch(to_charlist(uid), to_charlist(name))},
+           {:scope, :eldap.wholeSubtree()},
+           {:attributes, ['mail', 'email']},
+           {:timeout, @search_timeout}
+         ]) do
+      {:ok, {:eldap_search_result, [{:eldap_entry, _, attributes}], _}} ->
+        with {_, [mail]} <- List.keyfind(attributes, 'mail', 0) do
+          params = %{
+            email: :erlang.list_to_binary(mail),
+            name: name,
+            nickname: name,
+            password: password,
+            password_confirmation: password
+          }
+
+          changeset = User.register_changeset(%User{}, params)
+
+          case User.register(changeset) do
+            {:ok, user} -> user
+            error -> error
+          end
+        else
+          _ ->
+            Logger.error("Could not find LDAP attribute mail: #{inspect(attributes)}")
+            {:error, :ldap_registration_missing_attributes}
+        end
+
+      error ->
+        error
+    end
+  end
+end
diff --git a/lib/pleroma/web/auth/pleroma_authenticator.ex b/lib/pleroma/web/auth/pleroma_authenticator.ex
index 333446bef..94a19ad49 100644
--- a/lib/pleroma/web/auth/pleroma_authenticator.ex
+++ b/lib/pleroma/web/auth/pleroma_authenticator.ex
@@ -9,7 +9,14 @@ defmodule Pleroma.Web.Auth.PleromaAuthenticator do
   @behaviour Pleroma.Web.Auth.Authenticator
 
   def get_user(%Plug.Conn{} = conn) do
-    %{"authorization" => %{"name" => name, "password" => password}} = conn.params
+    {name, password} =
+      case conn.params do
+        %{"authorization" => %{"name" => name, "password" => password}} ->
+          {name, password}
+
+        %{"grant_type" => "password", "username" => name, "password" => password} ->
+          {name, password}
+      end
 
     with {_, %User{} = user} <- {:user, User.get_by_nickname_or_email(name)},
          {_, true} <- {:checkpw, Pbkdf2.checkpw(password, user.password_hash)} do
diff --git a/lib/pleroma/web/oauth/oauth_controller.ex b/lib/pleroma/web/oauth/oauth_controller.ex
index ec70b7ccc..d69383d40 100644
--- a/lib/pleroma/web/oauth/oauth_controller.ex
+++ b/lib/pleroma/web/oauth/oauth_controller.ex
@@ -5,7 +5,6 @@
 defmodule Pleroma.Web.OAuth.OAuthController do
   use Pleroma.Web, :controller
 
-  alias Comeonin.Pbkdf2
   alias Pleroma.Repo
   alias Pleroma.User
   alias Pleroma.Web.Auth.Authenticator
@@ -126,11 +125,10 @@ defmodule Pleroma.Web.OAuth.OAuthController do
 
   def token_exchange(
         conn,
-        %{"grant_type" => "password", "username" => name, "password" => password} = params
+        %{"grant_type" => "password"} = params
       ) do
-    with %App{} = app <- get_app_from_request(conn, params),
-         %User{} = user <- User.get_by_nickname_or_email(name),
-         true <- Pbkdf2.checkpw(password, user.password_hash),
+    with {_, {:ok, %User{} = user}} <- {:get_user, Authenticator.get_user(conn)},
+         %App{} = app <- get_app_from_request(conn, params),
          {:auth_active, true} <- {:auth_active, User.auth_active?(user)},
          scopes <- oauth_scopes(params, app.scopes),
          [] <- scopes -- app.scopes,
diff --git a/test/web/oauth/ldap_authorization_test.exs b/test/web/oauth/ldap_authorization_test.exs
new file mode 100644
index 000000000..570e41f3e
--- /dev/null
+++ b/test/web/oauth/ldap_authorization_test.exs
@@ -0,0 +1,187 @@
+# 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.LDAPAuthorizationTest do
+  use Pleroma.Web.ConnCase
+  alias Pleroma.Repo
+  alias Pleroma.Web.OAuth.Token
+  import Pleroma.Factory
+  import ExUnit.CaptureLog
+  import Mock
+
+  setup_all do
+    ldap_authenticator = Pleroma.Config.get([Pleroma.Web.Auth.Authenticator])
+    ldap_enabled = Pleroma.Config.get([:ldap, :enabled])
+
+    on_exit(fn ->
+      Pleroma.Config.put([Pleroma.Web.Auth.Authenticator], ldap_authenticator)
+      Pleroma.Config.put([:ldap, :enabled], ldap_enabled)
+    end)
+
+    Pleroma.Config.put([Pleroma.Web.Auth.Authenticator], Pleroma.Web.Auth.LDAPAuthenticator)
+    Pleroma.Config.put([:ldap, :enabled], true)
+
+    :ok
+  end
+
+  test "authorizes the existing user using LDAP credentials" do
+    password = "testpassword"
+    user = insert(:user, password_hash: Comeonin.Pbkdf2.hashpwsalt(password))
+    app = insert(:oauth_app, scopes: ["read", "write"])
+
+    host = Pleroma.Config.get([:ldap, :host]) |> to_charlist
+    port = Pleroma.Config.get([:ldap, :port])
+
+    with_mocks [
+      {:eldap, [],
+       [
+         open: fn [^host], [{:port, ^port}, {:ssl, false} | _] -> {:ok, self()} end,
+         simple_bind: fn _connection, _dn, ^password -> :ok end,
+         close: fn _connection ->
+           send(self(), :close_connection)
+           :ok
+         end
+       ]}
+    ] do
+      conn =
+        build_conn()
+        |> post("/oauth/token", %{
+          "grant_type" => "password",
+          "username" => user.nickname,
+          "password" => password,
+          "client_id" => app.client_id,
+          "client_secret" => app.client_secret
+        })
+
+      assert %{"access_token" => token} = json_response(conn, 200)
+
+      token = Repo.get_by(Token, token: token)
+
+      assert token.user_id == user.id
+      assert_received :close_connection
+    end
+  end
+
+  test "creates a new user after successful LDAP authorization" do
+    password = "testpassword"
+    user = build(:user)
+    app = insert(:oauth_app, scopes: ["read", "write"])
+
+    host = Pleroma.Config.get([:ldap, :host]) |> to_charlist
+    port = Pleroma.Config.get([:ldap, :port])
+
+    with_mocks [
+      {:eldap, [],
+       [
+         open: fn [^host], [{:port, ^port}, {:ssl, false} | _] -> {:ok, self()} end,
+         simple_bind: fn _connection, _dn, ^password -> :ok end,
+         equalityMatch: fn _type, _value -> :ok end,
+         wholeSubtree: fn -> :ok end,
+         search: fn _connection, _options ->
+           {:ok,
+            {:eldap_search_result, [{:eldap_entry, '', [{'mail', [to_charlist(user.email)]}]}],
+             []}}
+         end,
+         close: fn _connection ->
+           send(self(), :close_connection)
+           :ok
+         end
+       ]}
+    ] do
+      conn =
+        build_conn()
+        |> post("/oauth/token", %{
+          "grant_type" => "password",
+          "username" => user.nickname,
+          "password" => password,
+          "client_id" => app.client_id,
+          "client_secret" => app.client_secret
+        })
+
+      assert %{"access_token" => token} = json_response(conn, 200)
+
+      token = Repo.get_by(Token, token: token) |> Repo.preload(:user)
+
+      assert token.user.nickname == user.nickname
+      assert_received :close_connection
+    end
+  end
+
+  test "falls back to the default authorization when LDAP is unavailable" do
+    password = "testpassword"
+    user = insert(:user, password_hash: Comeonin.Pbkdf2.hashpwsalt(password))
+    app = insert(:oauth_app, scopes: ["read", "write"])
+
+    host = Pleroma.Config.get([:ldap, :host]) |> to_charlist
+    port = Pleroma.Config.get([:ldap, :port])
+
+    with_mocks [
+      {:eldap, [],
+       [
+         open: fn [^host], [{:port, ^port}, {:ssl, false} | _] -> {:error, 'connect failed'} end,
+         simple_bind: fn _connection, _dn, ^password -> :ok end,
+         close: fn _connection ->
+           send(self(), :close_connection)
+           :ok
+         end
+       ]}
+    ] do
+      log =
+        capture_log(fn ->
+          conn =
+            build_conn()
+            |> post("/oauth/token", %{
+              "grant_type" => "password",
+              "username" => user.nickname,
+              "password" => password,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+
+          assert %{"access_token" => token} = json_response(conn, 200)
+
+          token = Repo.get_by(Token, token: token)
+
+          assert token.user_id == user.id
+        end)
+
+      assert log =~ "Could not open LDAP connection: 'connect failed'"
+      refute_received :close_connection
+    end
+  end
+
+  test "disallow authorization for wrong LDAP credentials" do
+    password = "testpassword"
+    user = insert(:user, password_hash: Comeonin.Pbkdf2.hashpwsalt(password))
+    app = insert(:oauth_app, scopes: ["read", "write"])
+
+    host = Pleroma.Config.get([:ldap, :host]) |> to_charlist
+    port = Pleroma.Config.get([:ldap, :port])
+
+    with_mocks [
+      {:eldap, [],
+       [
+         open: fn [^host], [{:port, ^port}, {:ssl, false} | _] -> {:ok, self()} end,
+         simple_bind: fn _connection, _dn, ^password -> {:error, :invalidCredentials} end,
+         close: fn _connection ->
+           send(self(), :close_connection)
+           :ok
+         end
+       ]}
+    ] do
+      conn =
+        build_conn()
+        |> post("/oauth/token", %{
+          "grant_type" => "password",
+          "username" => user.nickname,
+          "password" => password,
+          "client_id" => app.client_id,
+          "client_secret" => app.client_secret
+        })
+
+      assert %{"error" => "Invalid credentials"} = json_response(conn, 400)
+      assert_received :close_connection
+    end
+  end
+end