Loosen restrictions for IAM user names

The only restriction for an IAM username is that it cannot start with
a '$'. An username that contains a ':' must escape it with another ':'
for use in a token for RTMP or SRT.

srt/srt.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/datarhei/core/v16/cluster/proxy"
+	enctoken "github.com/datarhei/core/v16/encoding/token"
 	"github.com/datarhei/core/v16/iam"
 	iamidentity "github.com/datarhei/core/v16/iam/identity"
 	"github.com/datarhei/core/v16/log"
@@ -493,15 +494,11 @@ func (s *server) findIdentityFromToken(key string) (string, error) {
 	var identity iamidentity.Verifier
 	var err error
 
-	var token string
-
-	before, after, found := strings.Cut(key, ":")
-	if !found {
+	username, token := enctoken.Unmarshal(key)
+	if len(username) == 0 {
 		identity = s.iam.GetDefaultVerifier()
-		token = before
 	} else {
-		identity, err = s.iam.GetVerifier(before)
-		token = after
+		identity, err = s.iam.GetVerifier(username)
 	}
 
 	if err != nil {