Google Mail IMAP response with padding makes auth parse error

[Abdillah]

Google responded to XOAUTH2 authentication with this base64 string with padding format (==),

S: + eyJzdGF0dXMiOiI0MDAiLCJzY2hlbWVzIjoiQmVhcmVyIiwic2NvcGUiOiJodHRwczovL21haWwuZ29vZ2xlLmNvbS8ifQ==

When I use online base64 tool, it reveals this text:

{"status":"400","schemes":"Bearer","scope":"https://mail.google.com/"}

The library unfortunately using base64::engine::general_purpose::STANDARD_NO_PAD that unable to parse the response and surfaced the error as error authenticating: Unable to parse authentication response.

[jonhoo]

Oh interesting — @soywod do you have more insight into this one? Should we switch which base64 engine configuration we use?

[Abdillah]

The response above specifically when failing the authentication. I haven't encounter any other encoded string.

The padding also exists (albeit in client request) in an official documentation:
https://developers.google.com/gmail/imap/xoauth2-protocol

[soywod]

Oh interesting — @soywod do you have more insight into this one? Should we switch which base64 engine configuration we use?

I can only say that imap-codec uses the STANDARD engine, and that I have no issue at app level to decode XOAUTH2 error. For which reasons imap uses the STANDARD_NO_PAD engine?