feat(security): implement ChainAuthenticator for sequential authentication

pkg/security/chain.go

@@ -0,0 +1,41 @@
+package security
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+)
+
+// ChainAuthenticator tries each authenticator in order, returning the first success.
+// Login and Logout are delegated to the primary authenticator.
+type ChainAuthenticator struct {
+	authenticators []Authenticator
+}
+
+// NewChainAuthenticator creates a ChainAuthenticator from the given authenticators.
+// At least one authenticator is required; the first is treated as primary for Login/Logout.
+func NewChainAuthenticator(primary Authenticator, rest ...Authenticator) *ChainAuthenticator {
+	return &ChainAuthenticator{
+		authenticators: append([]Authenticator{primary}, rest...),
+	}
+}
+
+func (c *ChainAuthenticator) Authenticate(r *http.Request) (*UserContext, error) {
+	var lastErr error
+	for _, a := range c.authenticators {
+		if uc, err := a.Authenticate(r); err == nil {
+			return uc, nil
+		} else {
+			lastErr = err
+		}
+	}
+	return nil, fmt.Errorf("all authenticators failed; last error: %w", lastErr)
+}
+
+func (c *ChainAuthenticator) Login(ctx context.Context, req LoginRequest) (*LoginResponse, error) {
+	return c.authenticators[0].Login(ctx, req)
+}
+
+func (c *ChainAuthenticator) Logout(ctx context.Context, req LogoutRequest) error {
+	return c.authenticators[0].Logout(ctx, req)
+}