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Area

oidc

Describe the bug

Endpoint POST http://keycloak.local/realms/myrealm/protocol/openid-connect/ext/par/request does not authenticate (returns 401) with client_secret_jwt when client_assertion and request keys are provided.

I.e. not compliant with OpenID Connect PAR specs and PAR's RFC-9126

Version

26.0.2

Regression

[ ] The issue is a regression

Expected behavior

A POST to http://keycloak.local/realms/myrealm/protocol/openid-connect/ext/par/request should return 201 with similar (values may vary) body response

```
{
"request_uri": "urn:ietf:params:oauth:request_uri:2277ae07-1bd1-4d43-84dc-2adb1680a016",
"expires_in": 60
}
```

when valid request, client_assertion, client_assertion_type, scope, response_type and client_id are provided.

Actual behavior

Keycloak does not authenticate ANY request to http://keycloak.local/realms/myrealm/protocol/openid-connect/ext/par/request when valid request, client_assertion, client_assertion_type, scope, response_type and client_id are provided. Instead it returns:

```
status: 401
resp body:

{
"error": "invalid_request",
"error_description": "Authentication failed."
}
```

How to Reproduce?

With any realm and client:

Perform a POST to endpoint /realms/myrealm/protocol/openid-connect/ext/par/request with content type as x-www-form-urlencoded and form with the following keys (defined in the Pushed Authorization Requests RFC) with valid values:

request, client_assertion, client_assertion_type, scope, response_type and client_id

Anything else?

All the calls were done based on RFC 9126 which refers to the Pushed Authorization Requests and OpenID Client Authentication specification.