Possible access role of a user.

UNSPECIFIED Not specified.
UNKNOWN Used for return value only. Represents value unknown in this version.
ADMIN Owns its account and can control the addition of other users.
STANDARD Can modify campaigns, but can't affect other users.
READ_ONLY Can view campaigns and account changes, but cannot make edits.
EMAIL_ONLY Role for "email only" access. Represents an email recipient rather than a true User entity.