Machine-to-machine authentication
Client credentials can be used for machine-to-machine communication authentication. Clients can authenticate themselves using service-accounts; standard client_id + client_secret is not sufficient. This behavior is due to providers only being able to have a single secret at any given time.
Note that authentik does treat a grant type of password the same as client_credentials to support applications which rely on a password grant.
Static authentication
Hence identification is based on service-accounts, and authentication is based on App-password tokens. These objects can be created in a single step using the Create Service account function.
An example request can look like this:
POST /application/o/token/ HTTP/1.1
Host: authentik.company
Content-Type: application/x-www-form-urlencoded
grant_type=client_credentials&
client_id=application_client_id&
username=my-service-account&
password=my-token
This will return a JSON response with an access_token, which is a signed JWT token. This token can be sent along requests to other hosts, which can then validate the JWT based on the signing key configured in authentik.
Starting with authentik 2024.4, it is also possible to encode the username and token of the user to authenticate with, separated with a colon, into a base64 string and pass it as client_secret value.
In addition to that, with authentik 2024.4 it is also possible to pass the configured client_secret value, which will automatically generate a service account user for which the JWT token will be issued.
JWT-authentication
Starting with authentik 2022.4, you can authenticate and get a token using an existing JWT.
(For readability we will refer to the JWT issued by the external issuer/platform as input JWT, and the resulting JWT from authentik as the output JWT)
To configure this, the certificate used to sign the input JWT must be created in authentik. The certificate is enough, a private key is not required. Afterwards, configure the certificate in the OAuth2 provider settings under Verification certificates.
Starting with authentik 2022.6, you can define a JWKS URL/raw JWKS data in OAuth Sources, and use those to verify the key instead of having to manually create a certificate in authentik for them. This method is still supported but will be removed in a later version.
With this configure, any JWT issued by the configured certificates can be used to authenticate:
POST /application/o/token/ HTTP/1.1
Host: authentik.company
Content-Type: application/x-www-form-urlencoded
grant_type=client_credentials&
client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer&
client_assertion=$inputJWT&
client_id=application_client_id
Alternatively, you can set the client_secret parameter to the $inputJWT, for applications which can set the password from a file but not other parameters.
Input JWTs are checked to be signed by any of the selected Verification certificates, and their exp attribute must not be now or in the past.
To do additional checks, you can use Expression policies:
return request.context["oauth_jwt"]["iss"] == "https://my.issuer"