Extend the implementation of mock openid server to take the `grant_type`
into consideration for the `/token` endpoint.
In addition to the previously supported `refresh_topen`, the
implementation now supports also `client_credentials`.
This is necessary to make it possible to use the mock server in
the `koji-osbuild` CI, because the builder plugin uses
`client_credentials` to get access token.
The implementation behaves in the following way:
- For `refresh_token` grant type, it takes the `refresh_token` value
from the request and adds it to the `rh-org-id` field in the custom
claim, which is part of the returned token.
- For `client_credentials` grant type, it takes the `client_secret`
value from the request and adds it to the `rh-org-id` field in the
custom claim, which is part of the returned token.
Requests without the supported `grant_type` set are rejected.
Modify affected test cases to specify `grant_type` when fetching a new
access token.
24c52c8d69