@property<EOL><INDENT>def birthday(self):<DEDENT>
return self._birthday<EOL>
Gets the birthday of this Customer.
The customer's birthday in RFC-3339 format. Year is optional, timezone and times are not allowed. Example: `0000-09-01T00:00:00-00:00` for a birthday on September 1st. `1998-09-01T00:00:00-00:00` for a birthday on September 1st 1998.

:return: The birthday of this Customer.
:rtype: str