Auth: Add IsClientEnabled and IsEnabled for the authn.Service and authn.Client interfaces (#86034)

* Add `Service. IsClientEnabled` and `Client.IsEnabled` functions

* Implement `IsEnabled` function for authn clients

* Implement `IsClientEnabled` function for authn services

pkg/services/authn/authn.go

@@ -94,6 +94,19 @@ type Service interface {
 
 	// RegisterClient will register a new authn.Client that can be used for authentication
 	RegisterClient(c Client)
+
+	// IsClientEnabled returns true if the client is enabled.
+	//
+	// The client lookup follows the same formats used by the `authn` package
+	// constants.
+	//
+	// For OAuth clients, use the `authn.ClientWithPrefix(name)` to get the provider
+	// name. Append the prefix `auth.client.{providerName}`.
+	//
+	// Example:
+	// - "saml" = "auth.client.saml"
+	// - "github" = "auth.client.github"
+	IsClientEnabled(client string) bool
 }
 
 type IdentitySynchronizer interface {
@@ -105,6 +118,8 @@ type Client interface {
 	Name() string
 	// Authenticate performs the authentication for the request
 	Authenticate(ctx context.Context, r *Request) (*Identity, error)
+	// IsEnabled returns the enabled status of the client
+	IsEnabled() bool
 }
 
 // ContextAwareClient is an optional interface that auth client can implement.