Description of problem:
Does WebSSO support application_credential as the authmethods like Keystone?
We recevied the below error:
```
Error: Unable to create application credential. Details
Invalid application credential: Could not find role assignment with role: 9fe2ff9ee4384b1894a90878d3e92bab, user or group: e74f576f45171f5a035d0c781596b64134bde4daca5614aac2c3de098c57e5aa, project, domain, or system: cfcc5ec8a9b542c5a168369559d70c92. (HTTP 400) (Request-ID: req-e657616c-411b-44a4-ab6f-a5882067fa74)
```

Version-Release number of selected component (if applicable):
17.1

How reproducible:

Steps to Reproduce:
1. Setup the OpenStack used RH-SSO
2. Tried to create a application credential after login the dashboard by RH-SSO
3.

Actual results:
```
Error: Unable to create application credential. Details
Invalid application credential: Could not find role assignment with role: 9fe2ff9ee4384b1894a90878d3e92bab, user or group: e74f576f45171f5a035d0c781596b64134bde4daca5614aac2c3de098c57e5aa, project, domain, or system: cfcc5ec8a9b542c5a168369559d70c92. (HTTP 400) (Request-ID: req-e657616c-411b-44a4-ab6f-a5882067fa74)
```

Expected results:
Can create application_credential from dashboard after after login the dashboard by RH-SSO

Additional info:
End user is our PSI cloud project.
The admin wants to know does WebSSO support application_credential as the authmethods like Keystone? Because we found this on the document mentioned application_credential on KeystoneAuthMethods only. Please kindly refer and comment this is a possible setup or not.