sasl structs: add shortcuts to for sasl.Mechanism

This will make sasl easier to use at callsites.

pkg/sasl/kerberos/kerberos.go

@@ -38,6 +38,17 @@ type Auth struct {
 	PersistAfterAuth bool
 }
 
+// AsMechanism returns a sasl mechanism that will use a as credentials for all
+// sasl sessions.
+//
+// This is a shortcut for using the Kerberos function and is useful when you do
+// not need to live-rotate credentials.
+func (a Auth) AsMechanism() sasl.Mechanism {
+	return Kerberos(func(context.Context) (Auth, error) {
+		return a, nil
+	})
+}
+
 // Kerberos returns a sasl mechanism that will call authFn whenever sasl
 // authentication is needed. The returned Auth is used for a single session.
 func Kerberos(authFn func(context.Context) (Auth, error)) sasl.Mechanism {

pkg/sasl/oauth/oauth.go

@@ -27,6 +27,17 @@ type Auth struct {
 	_internal struct{} // require explicit field initalization
 }
 
+// AsMechanism returns a sasl mechanism that will use a as credentials for all
+// sasl sessions.
+//
+// This is a shortcut for using the Oauth function and is useful when you do
+// not need to live-rotate credentials.
+func (a Auth) AsMechanism() sasl.Mechanism {
+	return Oauth(func(context.Context) (Auth, error) {
+		return a, nil
+	})
+}
+
 // Oauth returns an OAUTHBEARER sasl mechanism that will call authFn whenever
 // authentication is needed. The returned Auth is used for a single session.
 func Oauth(authFn func(context.Context) (Auth, error)) sasl.Mechanism {

pkg/sasl/plain/plain.go

@@ -22,6 +22,17 @@ type Auth struct {
 	_internal struct{} // require explicit field initalization
 }
 
+// AsMechanism returns a sasl mechanism that will use a as credentials for all
+// sasl sessions.
+//
+// This is a shortcut for using the Plain function and is useful when you do
+// not need to live-rotate credentials.
+func (a Auth) AsMechanism() sasl.Mechanism {
+	return Plain(func(context.Context) (Auth, error) {
+		return a, nil
+	})
+}
+
 // Plain returns a sasl mechanism that will call authFn whenever sasl
 // authentication is needed. The returned Auth is used for a single session.
 func Plain(authFn func(context.Context) (Auth, error)) sasl.Mechanism {

pkg/sasl/scram/scram.go

@@ -55,6 +55,28 @@ type Auth struct {
 	_internal struct{} // require explicit field initalization
 }
 
+// AsSha256Mechanism returns a sasl mechanism that will use a as credentials for
+// all sasl sessions.
+//
+// This is a shortcut for using the Sha256 function and is useful when you do
+// not need to live-rotate credentials.
+func (a Auth) AsSha256Mechanism() sasl.Mechanism {
+	return Sha256(func(context.Context) (Auth, error) {
+		return a, nil
+	})
+}
+
+// AsSha512Mechanism returns a sasl mechanism that will use a as credentials for
+// all sasl sessions.
+//
+// This is a shortcut for using the Sha512 function and is useful when you do
+// not need to live-rotate credentials.
+func (a Auth) AsSha512Mechanism() sasl.Mechanism {
+	return Sha512(func(context.Context) (Auth, error) {
+		return a, nil
+	})
+}
+
 // Sha256 returns a SCRAM-SHA-256 sasl mechanism that will call authFn
 // whenever authentication is needed. The returned Auth is used for a single
 // session.