[keycloak-user] Implicit Flow - Invalid grant_type

[Jonas Schönenberger]

Hi everyone

I would like to use the implicit flow with some of my services that use
Keycloak as their Identity-Provider. According to the documentation a token
can be obtained from the token endpoint with the implicit flow:

/realms/{realm-name}/protocol/openid-connect/token
> This is the URL endpoint for obtaining a temporary code in the
> Authorization Code Flow or for obtaining tokens via the Implicit Flow,
> Direct Grants, or Client Grants.


In the well-known config "implicit" is listed as a valid grant_type:

"grant_types_supported": [
>         "authorization_code",
>         "implicit",
>         "refresh_token",
>         "password",
>         "client_credentials"
>     ]


However calls to the above mentioned token endpoint fail with an "Invalid
grant_type" error when I set the "grant_type" to "implicit" and try to
fetch a token. Besides the implicit grant_type I handover the client_id of
my client, its redirect url, "id_token token" as "response_type" and as
"scope" "openid". Implicit flow is enabled on the clients I want to use
that flow with.

I had a look at the source code and it seems that the implicit grant_type
is not one of the accepted grant types:
https://github.com/keycloak/keycloak/blob/8b6979ac18b19eb47e618e05ccffdde0c9adb6ff/services/src/main/java/org/keycloak/protocol/oidc/endpoints/TokenEndpoint.java#L239

Does someone know how to obtain a token with the implicit flow from
Keycloak and whether it is possible through the above mentioned API at all?

Thank you for your support and Best Regards
Jonas