OAuth 2 Session

The OAuth2Session in Authlib was designed to be compatible with the one in requests-oauthlib. But now, there are some differences. This section is a guide on how to obtain an access token in OAuth 2 flow.


This OAuth2Session is a customized requests.Session. It shares the same API with requests. If you are using Flask, you may have interests in Flask OAuth Client. If you are using Django, please read Django OAuth Client.

OAuth2Session for Authorization Code

There are two steps in OAuth 2 to obtain an access token with authorization code grant type. Initialize the session for reuse:

>>> from authlib.client import OAuth2Session
>>> client_id = 'Your GitHub client ID'
>>> client_secret = 'Your GitHub client secret'
>>> scope = 'user:email'  # we want to fetch user's email
>>> session = OAuth2Session(client_id, client_secret, scope=scope)

You can assign a redirect_uri in case you want to specify the callback url.

Redirect to Authorization Endpoint

Unlike OAuth 1, there is no request token. The first step is to jump to the remote authorization server:

>>> authorize_url = 'https://github.com/login/oauth/authorize'
>>> uri, state = session.authorization_url(authorize_url)
>>> print(uri)

The OAuth2Session.authorization_url() returns a tuple of (uri, state), in real project, you should save the state for later use.

Now head over to the generated authorization url, and grant the authorization.

Fetch Access Token

The authorization server will redirect you back to your site with a code and state arguments:


Use OAuth2Session.fetch_access_token() to obtain access token. This method will also verify the state in case of CSRF attack:

>>> authorization_response = 'https://example.com/github?code=42..e9&state=d..t'
>>> access_token_url = 'https://github.com/login/oauth/access_token'
>>> token = session.fetch_access_token(access_token_url, authorization_response=authorization_response)
>>> print(token)
    'access_token': 'e..ad',
    'token_type': 'bearer',
    'scope': 'user:email'

Save this token to access users’ protected resources.

In real project, this session can not be re-used since you are redirected to another website. You need to create another session yourself:

>>> state = restore_previous_state()
>>> session = OAuth2Session(client_id, client_secret, state=state)
>>> session.fetch_access_token(access_token_url, authorization_response=authorization_response)

Authlib has a built-in Flask/Django integration. Learn from them.

OAuth2Session for Implicit

OAuth2Session supports implicit grant type. It can fetch the access token with the response_type of token:

>>> uri, state = session.authorization_url(authorize_url, response_type='token')
>>> print(uri)

Visit this link, and grant the authorization, the OAuth authoirzation server will redirect back to your redirect_uri, the response url would be something like:


Fetch access token from the fragment with OAuth2Session.fetch_access_token():

>>> token = session.fetch_access_token(authorization_response=authorization_response)
>>> # if you don't specify access token endpoint, it will fetch from fragment.
>>> print(token)
{'access_token': '2..WpA', 'token_type': 'bearer', 'expires_in': 3600}


GitHub doesn’t support token response type, try with other services.

OAuth2Session for Password

The password grant type is supported since Version 0.5. Use username and password to fetch the access token:

>>> token = session.fetch_access_token(token_url, username='a-name', password='a-password')

OAuth2Session for Client Credentials

The client_credentials grant type is supported since Version 0.5. If no code or no user info provided, it would be a client_credentials request. But it is suggested that you specify a grant_type for it:

>>> token = session.fetch_access_token(token_url)
>>> # or with grant_type
>>> token = session.fetch_access_token(token_url, grant_type='client_credentials')

Client Authentication

When fetching access token, the authorization server will require a client authentication, Authlib has provided a OAuth2ClientAuth which supports 3 methods defined by RFC7591:

  • client_secret_basic
  • client_secret_post
  • none

The default value is client_secret_basic. You can change the auth method with token_endpoint_auth_method:

>>> session = OAuth2Session(token_endpoint_auth_method='client_secret_post')

If the authorization server requires other means of authentication, you can construct an auth of requests, and pass it to fetch_access_token:

>>> auth = YourAuth(...)
>>> token = session.fetch_access_token(token_url, auth=auth, ...)

It is also possible to extend the client authentication method with register_client_auth_method(). Besides the default three authentication methods, there are more provided by Authlib. e.g.

  • client_secret_jwt
  • private_key_jwt

These two methods are defined by RFC7523 and OpenID Connect. Find more in Using JWTs for Client Authentication.

Access Protected Resources

Now you can access the protected resources. If you re-use the session, you don’t need to do anything:

>>> account_url = 'https://api.github.com/user'
>>> resp = session.get(account_url)
<Response [200]>
>>> resp.json()

The above is not the real flow, just like what we did in Fetch Access Token, we need to create another session ourselves:

>>> token = restore_access_token_from_database()
>>> # token is a dict which must contain ``access_token``, ``token_type``
>>> session = OAuth2Session(client_id, client_secret, token=token)
>>> account_url = 'https://api.github.com/user'
>>> resp = session.get(account_url)

Compliance Fix for non Standard

There are services that claimed they are providing OAuth API, but with a little differences. Some services even return with the wrong Content Type. Compliance hooks are provided to solve those problems:

  • access_token_response: invoked before token parsing.
  • refresh_token_response: invoked before refresh token parsing.
  • protected_request: invoked before making a request.

For instance, linkedin is using a oauth2_access_token parameter in query string to protect users’ resources, let’s fix it:

from authlib.common.urls import add_params_to_uri

def _non_compliant_param_name(url, headers, data):
    access_token = session.token.get('access_token')
    token = [('oauth2_access_token', access_token)]
    url = add_params_to_uri(url, token)
    return url, headers, data


If you find a non standard OAuth 2 services, and you can’t fix it. Please report it in GitHub issues.

OAuth 2 OpenID Connect

For services that support OpenID Connect, if a scope of openid is provided, the authorization server will return a value of id_token in response:

>>> from authlib.client import OAuth2Session
>>> client_id = 'Your Google client ID'
>>> client_secret = 'Your Google client secret'
>>> scope = 'openid email profile'
>>> session = OAuth2Session(client_id, client_secret, scope=scope)

The remote server may require other parameters for OpenID Connect requests, for instance, it may require a nonce parameter, in thise case, you need to generate it yourself, and pass it to authorization_url:

>>> from authlib.common.security import generate_token
>>> # remember to save this nonce for verification
>>> nonce = generate_token()
>>> session.authorization_url(url, redirect_uri='xxx', nonce=nonce, ...)

At the last step of session.fetch_access_token, the return value contains a id_token:

>>> resp = session.fetch_access_token(...)
>>> print(resp['id_token'])

This id_token is a JWT text, it can not be used unless it is parsed. Authlib has provided tools for parsing and validating OpenID Connect id_token:

>>> from authlib.specs.oidc import CodeIDToken
>>> from authlib.specs.rfc7519 import JWT
>>> # GET keys from https://www.googleapis.com/oauth2/v3/certs
>>> jwt = JWT()
>>> claims = jwt.decode(resp['id_token'], keys, claims_cls=CodeIDToken)
>>> claims.validate()

Get deep inside with JWT and CodeIDToken. Learn how to validate JWT claims at JSON Web Token.

There is a built-in Google app which supports OpenID Connect, checkout the source code in loginpass.


AssertionSession is a Requests Session for Assertion Framework of OAuth 2.0 Authorization Grants. It is also know as service account. A configured AssertionSession with handle token authorization automatically, which means you can just use it.

Take Google Service Account as an example, with the information in your service account JSON configure file:

import json
from authlib.client import AssertionSession

with open('MyProject-1234.json') as f:
    info = json.load(f)

token_url = conf['token_uri']
header = {'alg': 'RS256'}
key_id = conf.get('private_key_id')
if key_id:
    header['kid'] = key_id

# Google puts scope in payload
claims = {'scope': scope}

session = AssertionSession(

There is a ready to use GoogleServiceAccount in loginpass. You can also read these posts: