def METHOD_NAME(self, client_id: str, username: str, password: str) -> dict:
    """pbench-server realm user login on a specified client.
    Args:
        client_id: client_name to use in the request
        username: username of the user logging in
        password: OIDC password
    Returns:
        access_token json payload
        { 'access_token': <access_token>,
          'expires_in': 60, 'refresh_expires_in': 1800,
          'refresh_token': <refresh_token>,
          'token_type': 'Bearer',
          'not-before-policy': 0,
          'session_state': '8f558797-50e7-496d-bb45-3b5ac9fdcddb',
          'scope': 'profile email'}
    """
    url_path = f"/realms/{self.OIDC_REALM}/protocol/openid-connect/token"
    data = {
        "client_id": client_id,
        "grant_type": "password",
        "scope": "openid profile email",
        "username": username,
        "password": password,
    }
    return self.post(path=url_path, data=data).json()