Add error.code for the RPerror classes

[tabarra]

Is your feature request related to a problem? Please describe.
I would like to know when an code exchange error could be solved by synchronizing the host clock (90% of the problems my users have), but checking the error for error.message.startsWith('JWT expired, now') is a bit too hacky.

Describe the solution you'd like
Add the property code for the RPerror class with a small, likely stable, string indicating the issue.
Examples: jwt_nbf_invalid, jwt_expired.
Alternatively, you could add the an CLOCK_TOLERANCE property to any error that is related to this variable.

Describe alternatives you've considered

• Checking for the error message doesn't seems to stable;
• Reading the error.jwt and re-checking those cases is redundant;
• Adding some NTP client lib to make sure the clock is updated is too much of an overhead;
• Telling my users to update their clocks on every Code Exchange error;

Additional context
My open source project is very very often deployed on windows servers right after deployment, with some atrocious clocks.

• i have searched the issues tracker on github for similar requests and couldn't find anything related.

[panva]

@tabarra thanks for the suggestion.

Is it safe to say you want to be able to identify these four specific errors?

printf: ['too much time has elapsed since the last End-User authentication, max_age %i, auth_time: %i, now %i', maxAge, payload.auth_time, timestamp - this[CLOCK_TOLERANCE]],
printf: ['JWT issued too far in the past, now %i, iat %i', timestamp, payload.iat],
printf: ['JWT not active yet, now %i, nbf %i', timestamp + this[CLOCK_TOLERANCE], payload.nbf],
printf: ['JWT expired, now %i, exp %i', timestamp - this[CLOCK_TOLERANCE], payload.exp],

[tabarra]

Would be awesome to have code for all errors, since I would also like to handle timeout errors more gracefully, but those are more "edge cases".
Having an error code (or some other identifier) for those 4 would certainly help me out a lot!

And as always, thanks for the responsiveness @panva!

[tabarra]

Worked perfectly!
Once again, thanks for being so open to small tweaks!