Set token.Signature in ParseUnverified

[slickwilli]

Sets the token's Signature field in ParseUnverified as discussed in #413

[oxisto]

Sorry for the major delay on that, somehow this completely slipped through. What are your thoughts on that @mfridman? I would be ok with it.

[mfridman]

No issues from my end.

[oxisto]

No issues from my end.

Great. I will adjust this PR to avoid the double-setting of the signature though

[oxisto]

@mfridman please have another look at my optimised version

[samfoxcode]

@mfridman @oxisto - previously ParseUnverified did not validate the signature, but with this PR the signature is being validated by way of base64 and if the signature is not valid base64 it will error. Since this differs from the documented behavior of the method (ParseUnverified parses the token but **does not** validate the signature) should this be published as a breaking change and not a patch? Currently this was pushed in 5.3.1 as a patch but this is an unexpected behavior change that now causes an error to be returned.

I've opened an issue here as well: #499

[mfridman]

Thanks @samfoxcode we'll take a look!