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GitLab as an OAuth2 provider

This document covers using the OAuth2 protocol to allow other services access GitLab resources on user's behalf.

If you want GitLab to be an OAuth authentication service provider to sign into other services please see the OAuth2 provider documentation.

This functionality is based on doorkeeper gem.

Supported OAuth2 Flows

GitLab currently supports following authorization flows:

  • Web Application Flow - Most secure and common type of flow, designed for the applications with secure server-side.
  • Implicit Flow - This flow is designed for user-agent only apps (e.g. single page web application running on GitLab Pages).
  • Resource Owner Password Credentials Flow - To be used only for securely hosted, first-party services.

Please refer to OAuth RFC to find out in details how all those flows work and pick the right one for your use case.

Both web application and implicit flows require application to be registered first via /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 application credentials: Application ID and Client Secret - keep them secure.

Important: OAuth specification advises sending state parameter with each request to /oauth/authorize. We highly recommended to send a unique value with each request and validate it against the one in redirect request. This is important to prevent CSRF attacks. The state param really should have been a requirement in the standard!

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

Web Application Flow

Check RFC spec for a detailed flow description

1. Requesting authorization code

To request the authorization code, you should redirect the user to the /oauth/authorize endpoint with following GET parameters:

https://gitlab.example.com/oauth/authorize?client_id=APP_ID&redirect_uri=REDIRECT_URI&response_type=code&state=YOUR_UNIQUE_STATE_HASH

This will ask the user to approve the applications access to their account and then redirect back to the REDIRECT_URI you provided. The redirect will include the GET code parameter, for example:

http://myapp.com/oauth/redirect?code=1234567890&state=YOUR_UNIQUE_STATE_HASH

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

2. Requesting access token

Once you have the authorization code you can request an access_token using the code, to do that you can use any HTTP client. In the following example, we are using Ruby's rest-client:

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

# The response will be
{
 "access_token": "de6780bc506a0446309bd9362820ba8aed28aa506c71eedbe1c5c4f9dd350e54",
 "token_type": "bearer",
 "expires_in": 7200,
 "refresh_token": "8257e65c97202ed1726cf9571600918f3bffb2544b26e00a61df9897668c33a1"
}

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

Check RFC spec for a detailed flow description.

Unlike the web flow, the client receives an access token immediately as a result of the authorization request. The flow does not use client secret or authorization code because all of the application code and storage is easily accessible, therefore secrets can leak easily.

Important: Avoid using this flow for applications that store data outside of the GitLab instance. If you do, make sure to verify application id associated with access token before granting access to the data (see /oauth/token/info).

1. Requesting access token

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

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

This will ask the user to approve the applications access to their account and then redirect back to the REDIRECT_URI you provided. The redirect will include a fragment with access_token as well as token details in GET parameters, for example:

http://myapp.com/oauth/redirect#access_token=ABCDExyz123&state=YOUR_UNIQUE_STATE_HASH&token_type=bearer&expires_in=3600

Resource Owner Password Credentials

Check RFC spec for a detailed flow description.

Deprecation notice: Starting in GitLab 8.11, the Resource Owner Password Credentials has been disabled for users with two-factor authentication turned on. These users can access the API using personal access tokens 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 (e.g. the client is part of the device operating system or a highly privileged application), and when other authorization grant types are not available (such as an authorization code).

Important: Never store the users credentials and only use this grant type when your client is deployed to a trusted environment, in 99% of cases personal access tokens 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.

1. Requesting access token

POST request to /oauth/token with parameters:

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

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

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

For testing you can use the oauth2 ruby gem:

client = OAuth2::Client.new('the_client_id', 'the_client_secret', :site => "http://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 a behalf of a user. You can pass the token either as GET parameter

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

or you can put the token to the Authorization header:

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