CredentialsManager function to clear and revoke the refresh token

[stevehobbsdev]

Changes

This PR adds a new method revoke to CredentialsManager, which boths clears credentials and revokes the refresh token, if available. It accepts a callback for when the revocation call has finished.

When called, it first checks to make sure that it has:

• Valid credentials stored
• A refresh token

If there is no refresh token, then the credentials are cleared as normal without the revoke endpoint being called.

Otherwise, it uses its internal instance of Authentication to call the revoke endpoint, passing the refresh token. If this call is successful, the credentials are cleared. If not, the credentials remain and the callback is invoked with an error.

Use Case

The revoke function could be used in most cases where the user's session is to be cleared, as it's designed to clear credentials even if there is no refresh token. Using clear would be beneficial if the session is to be cleared but the developer explicitly does not want to revoke the refresh token.

Usage

The PR adds one method to the CredentialsManager API:

credentialsManager.revoke { error in
    guard error == nil else {
        print("Failed to revoke the refresh token: \(error)")
    }

    print("Token revoked and credentials cleared!")
}

Testing

• This change adds unit test coverage
• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines
• All existing and new tests complete without errors
• All active GitHub checks have passed

[stevehobbsdev]

The unit tests need a little re-working to try and avoid the use of the now-deprecated clear() method.

[cocojoe]

@stevehobbsdev fix your tests, appear to be breaking for everything other than tvOS in Swift 5 😄 So they would also be failing locally then? Let me know if you want to pair on this.

[cocojoe]

Few areas to discuss