SCRAM plus variants

[sjaeckel]

Add support for SASL methods SCRAM-SHA1-PLUS and SCRAM-SHA256-PLUS.

Fixes #133

[Neustradamus]

@sjaeckel: I have only seen your PR today!

Good job! :)

Only one remark, can you add "tls-server-end-point" support too?

It is needed for security and for example here (In more RFCs):

• XEP-0388: Extensible SASL Profile: https://xmpp.org/extensions/xep-0388.html
• XEP-0440: SASL Channel-Binding Type Capability: https://xmpp.org/extensions/xep-0440.html
• XEP-0474: SASL SCRAM Downgrade Protection: https://xmpp.org/extensions/xep-0474.html
• XEP-0480: SASL Upgrade Tasks: https://xmpp.org/extensions/xep-0480.html
• draft-melnikov-sasl2: Extensible Simple Authentication and Security Layer (SASL): https://datatracker.ietf.org/doc/html/draft-melnikov-sasl2

There is a talk about it on Standards ML:

• https://mail.jabber.org/hyperkitty/list/standards@xmpp.org/thread/MBNEF3NMA3UDD4SKULEY7AZCA3TV4I5P/

Thanks in advance.