Allow Client Credentials grant flow to specify the user that the token will be granted as

Currently the token is issued as the user that created the OAuth2 application. It might have too broad permission when it's done by an Administrator.

Fixed in

• Liferay CE Plugin for OAuth 2.0 version 2.0.0 and higher for Liferay Portal 7.2
• Liferay Plugin for OAuth 2.0 version 2.0.0 and higher for Liferay DXP 7.2

How to achieve the same behavior in 7.1:

1. Create a new Regular Role called "OAuth2 App Creator"
2. Define the following permissions for this new role:
   • OAuth 2 Administration > Access in Control Panel
   • OAuth 2 Administration > Add OAuth 2 Application
   • Portal: View Control Panel Menu (granted automatically)
3. Assign the new role to a User who you want to add the OAuth2 app on behalf of. This will be the user that the token will be granted as
4. Impersonate that user and add the OAuth2 app
5. Revoke the "OAuth2 App Creator" role from this user