Enum that represents the types of invalid token reasons.
Values:
INVALID_REASON_UNSPECIFIED (0):
Default unspecified type.
UNKNOWN_INVALID_REASON (1):
If the failure reason was not accounted for.
MALFORMED (2):
The provided user verification token was
malformed.
EXPIRED (3):
The user verification token had expired.
DUPE (4):
The user verification had already been seen.
MISSING (5):
The user verification token was not present.
BROWSER_ERROR (6):
A retriable error (such as network failure)
occurred on the browser. Could easily be
simulated by an attacker.
