gitlab-org--gitlab-foss/doc/api/oauth2.md

---
type: reference, howto
stage: Manage
group: Access
info: To determine the technical writer assigned to the Stage/Group associated   with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---

# GitLab as an OAuth2 provider

This document covers using the [OAuth2](https://oauth.net/2/) protocol to allow
other services to access GitLab resources on user's behalf.

If you want GitLab to be an OAuth authentication service provider to sign into
other services, see the [OAuth2 authentication service provider](../integration/oauth_provider.md)
documentation. This functionality is based on the
[doorkeeper Ruby gem](https://github.com/doorkeeper-gem/doorkeeper).

## Supported OAuth2 flows

GitLab currently supports the following authorization flows:

- **Authorization code with [Proof Key for Code Exchange (PKCE)](https://tools.ietf.org/html/rfc7636):**
  Most secure. Without PKCE, you'd have to include client secrets on mobile clients,
  and is recommended for both client and server aoos.
- **Authorization code:** Secure and common flow. Recommended option for secure
  server-side apps.
- **Implicit grant:** Originally designed for user-agent only apps, such as
  single page web apps running on GitLab Pages).
  The [IETF](https://tools.ietf.org/html/draft-ietf-oauth-security-topics-09#section-2.1.2)
  recommends against Implicit grant flow.
- **Resource owner password credentials:** To be used **only** for securely
  hosted, first-party services. GitLab recommends against use of this flow.

The draft specification for [OAuth 2.1](https://oauth.net/2.1/) specifically omits both the
Implicit grant and Resource Owner Password Credentials flows.
  it will be deprecated in the next OAuth specification version.

Refer to the [OAuth RFC](https://tools.ietf.org/html/rfc6749) to find out
how all those flows work and pick the right one for your use case.

Both **authorization code** (with or without PKCE) and **implicit grant** flows require `application` to be
registered first via the `/profile/applications` page in your user's account.
During registration, by enabling proper scopes, you can limit the range of
resources which the `application` can access. Upon creation, you'll obtain the
`application` credentials: _Application ID_ and _Client Secret_ - **keep them secure**.

### Prevent CSRF attacks

To [protect redirect-based flows](https://tools.ietf.org/id/draft-ietf-oauth-security-topics-13.html#rec_redirect),
the OAuth specification recommends the use of "One-time use CSRF tokens carried in the state
parameter, which are securely bound to the user agent", with each request to the
`/oauth/authorize` endpoint. This can prevent
[CSRF attacks](https://wiki.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)).

### Use HTTPS in production

For production, please use HTTPS for your `redirect_uri`.
For development, GitLab allows insecure HTTP redirect URIs.

As OAuth2 bases its security entirely on the transport layer, you should not use unprotected
URIs. For more information, see the [OAuth 2.0 RFC](https://tools.ietf.org/html/rfc6749#section-3.1.2.1)
and the [OAuth 2.0 Threat Model RFC](https://tools.ietf.org/html/rfc6819#section-4.4.2.1).
These factors are particularly important when using the
[Implicit grant flow](#implicit-grant-flow), where actual credentials are included in the `redirect_uri`.

In the following sections you will find detailed instructions on how to obtain
authorization with each flow.

### Authorization code with Proof Key for Code Exchange (PKCE)

The [PKCE RFC](https://tools.ietf.org/html/rfc7636#section-1.1) includes a
detailed flow description, from authorization request through access token.
The following steps describe our implementation of the flow.

The Authorization code with PKCE flow, PKCE for short, makes it possible to securely perform
the OAuth exchange of client credentials for access tokens on public clients.

Before starting the flow, generate the `STATE`, the `CODE_VERIFIER` and the `CODE_CHALLENGE`.

- The `STATE` a value that can't be predicted used by the client to maintain
  state between the request and callback. It should also be used as a CSRF token.
- The `CODE_VERIFIER` is a random string, between 43 and 128 characters in length,
  which use the characters `A-Z`, `a-z`, `0-9`, `-`, `.`, `_`, and `~`.
- The `CODE_CHALLENGE` is an URL-safe base64-encoded string of the SHA256 hash of the
  `CODE_VERIFIER`
  - In Ruby, you can set that up with `Base64.urlsafe_encode64(Digest::SHA256.digest(CODE_VERIFIER))`.

1. Request authorization code. To do that, you should redirect the user to the
   `/oauth/authorize` page with the following query parameters:

   ```plaintext
   https://gitlab.example.com/oauth/authorize?client_id=APP_ID&redirect_uri=REDIRECT_URI&response_type=code&state=YOUR_UNIQUE_STATE_HASH&scope=REQUESTED_SCOPES&code_challenge=CODE_CHALLENGE&code_challenge_method=S256
   ```

   This page asks the user to approve the request from the app to access their
   account based on the scopes specified in `REQUESTED_SCOPES`. The user is then
   redirected back to the specified `REDIRECT_URI`. The [scope parameter](https://github.com/doorkeeper-gem/doorkeeper/wiki/Using-Scopes#requesting-particular-scopes)
   is a space separated list of scopes associated with the user.
   For example,`scope=read_user+profile` requests the `read_user` and `profile` scopes.
   The redirect includes the authorization `code`, for example:

   ```plaintext
   https://example.com/oauth/redirect?code=1234567890&state=YOUR_UNIQUE_STATE_HASH
   ```

1. With the authorization `code` returned from the previous request (denoted as
   `RETURNED_CODE` in the following example), you can request an `access_token`, with
   any HTTP client. The following example uses Ruby's `rest-client`:

   ```ruby
   parameters = 'client_id=APP_ID&client_secret=APP_SECRET&code=RETURNED_CODE&grant_type=authorization_code&redirect_uri=REDIRECT_URI&code_verifier=CODE_VERIFIER'
   RestClient.post 'https://gitlab.example.com/oauth/token', parameters
   ```

   Example response:

   ```json
   {
    "access_token": "de6780bc506a0446309bd9362820ba8aed28aa506c71eedbe1c5c4f9dd350e54",
    "token_type": "bearer",
    "expires_in": 7200,
    "refresh_token": "8257e65c97202ed1726cf9571600918f3bffb2544b26e00a61df9897668c33a1",
    "created_at": 1607635748
   }
   ```

NOTE:
The `redirect_uri` must match the `redirect_uri` used in the original
authorization request.

You can now make requests to the API with the access token.

### Authorization code flow

NOTE:
Check the [RFC spec](https://tools.ietf.org/html/rfc6749#section-4.1) for a
detailed flow description.

The authorization code flow is essentially the same as
[authorization code flow with PKCE](#authorization-code-with-proof-key-for-code-exchange-pkce),

1. Request authorization code. To do that, you should redirect the user to the
   `/oauth/authorize` endpoint with the following GET parameters:

   ```plaintext
   https://gitlab.example.com/oauth/authorize?client_id=APP_ID&redirect_uri=REDIRECT_URI&response_type=code&state=STATE&scope=REQUESTED_SCOPES
   ```

   This will ask the user to approve the applications access to their account
   based on the scopes specified in `REQUESTED_SCOPES` and then redirect back to
   the `REDIRECT_URI` you provided. The [scope parameter](https://github.com/doorkeeper-gem/doorkeeper/wiki/Using-Scopes#requesting-particular-scopes)
   is a space separated list of scopes you want to have access to (e.g. `scope=read_user+profile`
   would request `read_user` and `profile` scopes). The redirect will
   include the GET `code` parameter, for example:

   ```plaintext
   https://example.com/oauth/redirect?code=1234567890&state=STATE
   ```

   You should then use `code` to request an access token.

1. After you have the authorization code you can request an `access_token` using the
   code. You can do that by using any HTTP client. In the following example,
   we are using Ruby's `rest-client`:

   ```ruby
   parameters = 'client_id=APP_ID&client_secret=APP_SECRET&code=RETURNED_CODE&grant_type=authorization_code&redirect_uri=REDIRECT_URI'
   RestClient.post 'https://gitlab.example.com/oauth/token', parameters
   ```

   Example response:

   ```json
   {
    "access_token": "de6780bc506a0446309bd9362820ba8aed28aa506c71eedbe1c5c4f9dd350e54",
    "token_type": "bearer",
    "expires_in": 7200,
    "refresh_token": "8257e65c97202ed1726cf9571600918f3bffb2544b26e00a61df9897668c33a1",
    "created_at": 1607635748
   }
   ```

NOTE:
The `redirect_uri` must match the `redirect_uri` used in the original
authorization request.

You can now make requests to the API with the access token returned.

### Implicit grant flow

NOTE:
For a detailed flow diagram, see the [RFC specification](https://tools.ietf.org/html/rfc6749#section-4.2).

WARNING:
The Implicit grant flow is inherently insecure. The IETF plans to remove it in
[OAuth 2.1](https://oauth.net/2.1/).

We recommend that you use [Authorization code with PKCE](#authorization-code-with-proof-key-for-code-exchange-pkce) instead. If you choose to use Implicit flow, be sure to verify the
`application id` (or `client_id`) associated with the access token before granting
access to the data, as described in [Retrieving the token information](#retrieving-the-token-information)).

Unlike the authorization code flow, the client receives an `access token`
immediately as a result of the authorization request. The flow does not use
the client secret or the authorization code because all of the application code
and storage is easily accessible on client browsers and mobile devices.

To request the access token, you should redirect the user to the
`/oauth/authorize` endpoint using `token` response type:

```plaintext
https://gitlab.example.com/oauth/authorize?client_id=APP_ID&redirect_uri=REDIRECT_URI&response_type=token&state=YOUR_UNIQUE_STATE_HASH&scope=REQUESTED_SCOPES
```

This will ask the user to approve the applications access to their account
based on the scopes specified in `REQUESTED_SCOPES` and then redirect back to
the `REDIRECT_URI` you provided. The [scope parameter](https://github.com/doorkeeper-gem/doorkeeper/wiki/Using-Scopes#requesting-particular-scopes)
   is a space separated list of scopes you want to have access to (e.g. `scope=read_user+profile`
would request `read_user` and `profile` scopes). The redirect
will include a fragment with `access_token` as well as token details in GET
parameters, for example:

```plaintext
https://example.com/oauth/redirect#access_token=ABCDExyz123&state=YOUR_UNIQUE_STATE_HASH&token_type=bearer&expires_in=3600
```

### Resource owner password credentials flow

NOTE:
Check the [RFC spec](https://tools.ietf.org/html/rfc6749#section-4.3) for a
detailed flow description.

NOTE:
The Resource Owner Password Credentials is disabled for users with [two-factor
authentication](../user/profile/account/two_factor_authentication.md) turned on.
These users can access the API using [personal access tokens](../user/profile/personal_access_tokens.md)
instead.

In this flow, a token is requested in exchange for the resource owner credentials
(username and password).

The credentials should only be used when:

- There is a high degree of trust between the resource owner and the client. For
  example, the client is part of the device operating system or a highly
  privileged application.
- Other authorization grant types are not available (such as an authorization code).

WARNING:
Never store the user's credentials and only use this grant type when your client
is deployed to a trusted environment, in 99% of cases
[personal access tokens](../user/profile/personal_access_tokens.md) are a better
choice.

Even though this grant type requires direct client access to the resource owner
credentials, the resource owner credentials are used for a single request and
are exchanged for an access token. This grant type can eliminate the need for
the client to store the resource owner credentials for future use, by exchanging
the credentials with a long-lived access token or refresh token.

To request an access token, you must make a POST request to `/oauth/token` with
the following parameters:

```json
{
  "grant_type"    : "password",
  "username"      : "user@example.com",
  "password"      : "secret"
}
```

Also you must use HTTP Basic authentication using the `client_id` and`client_secret`
values to authenticate the client that performs a request.

Example cURL request:

```shell
echo 'grant_type=password&username=<your_username>&password=<your_password>' > auth.txt
curl --data "@auth.txt" --user client_id:client_secret --request POST "https://gitlab.example.com/oauth/token"
```

Then, you'll receive the access token back in the response:

```json
{
  "access_token": "1f0af717251950dbd4d73154fdf0a474a5c5119adad999683f5b450c460726aa",
  "token_type": "bearer",
  "expires_in": 7200
}
```

By default, the scope of the access token is `api`, which provides complete read/write access.

For testing, you can use the `oauth2` Ruby gem:

```ruby
client = OAuth2::Client.new('the_client_id', 'the_client_secret', :site => "https://example.com")
access_token = client.password.get_token('user@example.com', 'secret')
puts access_token.token
```

## Access GitLab API with `access token`

The `access token` allows you to make requests to the API on behalf of a user.
You can pass the token either as GET parameter:

```plaintext
GET https://gitlab.example.com/api/v4/user?access_token=OAUTH-TOKEN
```

or you can put the token to the Authorization header:

```shell
curl --header "Authorization: Bearer OAUTH-TOKEN" "https://gitlab.example.com/api/v4/user"
```

## Retrieving the token information

To verify the details of a token, use the `token/info` endpoint provided by the Doorkeeper gem.
For more information, see [`/oauth/token/info`](https://github.com/doorkeeper-gem/doorkeeper/wiki/API-endpoint-descriptions-and-examples#get----oauthtokeninfo).

You must supply the access token, either:

- As a parameter:

   ```plaintext
   GET https://gitlab.example.com/oauth/token/info?access_token=<OAUTH-TOKEN>
   ```

- In the Authorization header:

   ```shell
   curl --header "Authorization: Bearer <OAUTH-TOKEN>" "https://gitlab.example.com/oauth/token/info"
   ```

The following is an example response:

```json
{
    "resource_owner_id": 1,
    "scope": ["api"],
    "expires_in": null,
    "application": {"uid": "1cb242f495280beb4291e64bee2a17f330902e499882fe8e1e2aa875519cab33"},
    "created_at": 1575890427
}
```

### Deprecated fields

The fields `scopes` and `expires_in_seconds` are included in the response.

These are aliases for `scope` and `expires_in` respectively, and have been included to
prevent breaking changes introduced in [doorkeeper 5.0.2](https://github.com/doorkeeper-gem/doorkeeper/wiki/Migration-from-old-versions#from-4x-to-5x).

Don't rely on these fields as they will be removed in a later release.