Allow expires_in equals 0

[artad]

Some services (http://vk.com, no expiration) return "expires_in" equals 0 and no "expires".
In this case:
!empty($options['expires_in']) == FALSE
!empty($options['expires']) == FALSE
and expires property remain NULL

[coveralls]

Coverage remained the same at 100.0% when pulling a17b6fc on artad:master into 4aec352 on thephpleague:master.

[coveralls]

Coverage remained the same at 100.0% when pulling a17b6fc on artad:master into 4aec352 on thephpleague:master.

[coveralls]

Coverage remained the same at 100.0% when pulling a17b6fc on artad:master into 4aec352 on thephpleague:master.

[ramsey]

Thanks, @artad.

This seems to comply with the definition of "expires_in" in appendix A.14. of RFC 6749:

expires-in = 1*DIGIT

It can be 1 or more DIGIT, where RFC 5234 defines DIGIT as

     DIGIT          =  %x30-39
                            ; 0-9

Any concerns, @shadowhand?

[shadowhand]

LGTM.

[ramsey]

Thanks!

[artad]

Thanks for your attention

[ghost]

This breaks the code tho, hasExpired() uses the PHP empty() function to determine if expires is set or not. 0 is considered empty using that function.

As is, it yields the following error

RuntimeException: "expires" is not set on the token in vendor/league/oauth2-client/src/Token/AccessToken.php on line 174