implement SASL OAUTHBEARER and draft/bearer (#2122)

* implement SASL OAUTHBEARER and draft/bearer
* Upgrade JWT lib
* Fix an edge case in SASL EXTERNAL
* Accept longer SASL responses
* review fix: allow multiple token definitions
* enhance tests
* use SASL utilities from irc-go
* test expired tokens

vendor/github.com/golang-jwt/jwt/v5/claims.go

@@ -0,0 +1,16 @@
+package jwt
+
+// Claims represent any form of a JWT Claims Set according to
+// https://datatracker.ietf.org/doc/html/rfc7519#section-4. In order to have a
+// common basis for validation, it is required that an implementation is able to
+// supply at least the claim names provided in
+// https://datatracker.ietf.org/doc/html/rfc7519#section-4.1 namely `exp`,
+// `iat`, `nbf`, `iss`, `sub` and `aud`.
+type Claims interface {
+	GetExpirationTime() (*NumericDate, error)
+	GetIssuedAt() (*NumericDate, error)
+	GetNotBefore() (*NumericDate, error)
+	GetIssuer() (string, error)
+	GetSubject() (string, error)
+	GetAudience() (ClaimStrings, error)
+}