String value on expires_at results in exception

[JTStoll]

Describe the bug

When a token passes a String date field for expires_at, an exception is thrown, making it impossible to parse the token.

My team encountered this attempting to do an OAuth flow with Square (https://squareup.com), so this is certainly happening in out in the wild. Square passes a string date, something like '2021-JUN-12 13:42:36'.

In addition, it looks as though this same issue would happen if a string were passed on exipires_in, though that seems much less likely. Still, a check on the data type wouldn't hurt.

How to reproduce

Attempt to parse a token with a String expires_at. An exception will be thrown.

Expected behavior

One of two things should happen. Either we should just ignore the expires_at field, or we should try to parse it as a datetime.

Personally, I'd go with the option of just ignoring any non-Integers in this field.

Additional context

The line this is happening on is here:

oauthlib/oauthlib/oauth2/rfc6749/clients/base.py

Line 515 in b69fa53

if 'expires_at' in response:

Either catch the exception or just checking that the expires_at field is valid before casting it as an int.

[auvipy]

can you atleast provide or start with a failing test case?

[JTStoll]

I can do one better. We've come up with a PR to fix this:

#783

[JonathanHuot]

Fixed in #783