Specify NUT-22 authA serialization

[robwoodgate]

NUT-22 does not specify the base64 encoding variant to use.

CDK uses general_purpose::URL_SAFE, which requires base64 URL with padding .

This PR requires mints to support both padded and unpadded forms (as per #147).

Implementation

• Cashu-TS: fix(auth): use ensureCAT if available so token is refreshed cashu-ts#529 (sends padded)
• CDK: auth token should not be required to have padding cdk#1740
• Nutshell: Confirm NUT-22 authA serialization nutshell#919

NOTE: This was not an issue prior to keysets v2, as keyset v1 IDs (16 chars) produced serialized BAT JSON of exactly 174 bytes, and 174 % 3 = 0 — so base64 encoding never produced any padding before.

[thesimplekid]

@robwoodgate looks like what I told you was wrong. We did not restrict the spec for the normal tokens. So I think we should do the same here and cdk should be changed to be less restrictive.

#147

[robwoodgate]

@robwoodgate looks like what I told you was wrong. We did not restrict the spec for the normal tokens. So I think we should do the same here and cdk should be changed to be less restrictive.

#147

@thesimplekid - that is even better. I've tweaked the spec to say mints MUST support both forms.

I'll leave Cashu-TS on padded, as that is backwards compatible with CDK <= 0.15.2

Please can you raise a ticket to sort CDK and pop it on this PR when ready.