How Keycloack grant access to a client only to a group of users

How can i with Keycloack grant access to a client only to a group of users using open-id and OAuth 2.0
Thanks

Hello,

i would like to get the same answer for all the auth types. Both OpenID and SAML.

What i need is to give users group and use that to select, who can access what client.

Or is there any other solution how to determine, who can access that or that client in a single realm?

Thank you!