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How to obtain authorization from a user and perform actions on their behalf.

Last modified Sun Dec 18, 2022
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Scopes explained

When we registered our app and when we will authorize our user, we need to define what exactly our generated token will have permission to do. This is done through the use of OAuth scopes. Each API method has an associated scope, and can only be called if the token being used for authorization has been generated with the corresponding scope.

Scopes must be a subset. When we created our app, we specified read write push – we could request all available scopes by specifying read write push, but it is a better idea to only request what your app will actually need through granular scopes. See OAuth Scopes for a full list of scopes. Each API method’s documentation will also specify the OAuth access level and scope required to call it.

Example authorization code flow

This is similar to the authentication flow from before, but this time, we need to obtain authorization from a user as well.

Client ID and secret

First, if you have not already registered a client application, then see Creating our application on the previous page or go directly to POST /api/v1/apps for the full documentation of that method. We will need the client_id and client_secret for our application.

Authorize the user

To authorize a user, request GET /oauth/authorize in a browser with the following query parameters:

https://mastodon.example/oauth/authorize
?client_id=CLIENT_ID
&scope=read+write+push
&redirect_uri=urn:ietf:wg:oauth:2.0:oob
&response_type=code

Note the following:

  • client_id was obtained when registering our application.
  • scope must be a subset of our registered app’s registered scopes. It is a good idea to only request what you need. See OAuth Scopes for more information.
  • redirect_uri is one of the URIs we registered with our app. We are still using “out of band” for this example, which means we will have to manually copy and paste the resulting code, but if you registered your application with a URI that you control, then the code will be returned as a query parameter code and can be logged by your request handler. See the response section of the API method documentation for more information on this.

Obtain the token

Now that we have an authorization code, let’s obtain an access token that will authenticate our requests as the authorized user. To do so, use POST /oauth/token like before, but pass the authorization code we just obtained:

curl -X POST \
	-F 'client_id=your_client_id_here' \
	-F 'client_secret=your_client_secret_here' \
	-F 'redirect_uri=urn:ietf:wg:oauth:2.0:oob' \
	-F 'grant_type=authorization_code' \
	-F 'code=user_authzcode_here' \
	-F 'scope=read write push' \
	https://mastodon.example/oauth/token

Note the following:

  • client_id and client_secret were provided in the response text when you registered your application.
  • redirect_uri must be one of the URIs defined when registering the application.
  • We are requesting a grant_type of authorization_code, which still defaults to giving us the read scope. However, while authorizing our user, we requested a certain scope – pass the exact same value here.
  • The code can only be used once. If you need to obtain a new token, you will need to have the user authorize again by repeating the above Authorize the user step.

The response of this method is a Token entity. We will need the access_token value. Once you have the access token, save it in your local cache. To use it in requests, add the HTTP header Authorization: Bearer ... to any API call that requires OAuth (i.e., one that is not publicly accessible). Let’s verify that our obtained credentials are working by calling GET /api/v1/accounts/verify_credentials:

curl \
	-H 'Authorization: Bearer our_access_token_here' \
	https://mastodon.example/api/v1/accounts/verify_credentials

If we’ve obtained our token and formatted our request correctly, we should see our details returned to us as an Account entity, with the source parameter included.

Performing actions as the authorized user

With our OAuth token for the authorized user, we can now perform any action as that user that is within our token’s scope.

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