Add an AssertionHandler to the middleware

.github/workflows/lint.yml

@@ -11,8 +11,8 @@ jobs:
     name: Run golangci-lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v2
+        uses: golangci/golangci-lint-action@v3
         with:
           version: v1.46.2

samlsp/basic_assertion_handler.go

@@ -0,0 +1,17 @@
+package samlsp
+
+import (
+	"github.com/crewjam/saml"
+)
+
+var _ SamlAssertionHandler = BasicSamlAssertionHandler{}
+
+// BasicSamlAssertionHandler is an implementation of SamlAssertionHandler that has
+// an empty HandleAssertion function to retain useability.
+type BasicSamlAssertionHandler struct{}
+
+// HandleAssertion is called and passed saml assertion
+// this can add extra functionality and should return any error that occurs.
+func (as BasicSamlAssertionHandler) HandleAssertion(assertion *saml.Assertion) error {
+	return nil
+}

samlsp/middleware.go

@@ -39,12 +39,13 @@ import (
 // SAML service provider already has a private key, we borrow that key
 // to sign the JWTs as well.
 type Middleware struct {
-	ServiceProvider saml.ServiceProvider
-	OnError         func(w http.ResponseWriter, r *http.Request, err error)
-	Binding         string // either saml.HTTPPostBinding or saml.HTTPRedirectBinding
-	ResponseBinding string // either saml.HTTPPostBinding or saml.HTTPArtifactBinding
-	RequestTracker  RequestTracker
-	Session         SessionProvider
+	ServiceProvider  saml.ServiceProvider
+	OnError          func(w http.ResponseWriter, r *http.Request, err error)
+	Binding          string // either saml.HTTPPostBinding or saml.HTTPRedirectBinding
+	ResponseBinding  string // either saml.HTTPPostBinding or saml.HTTPArtifactBinding
+	RequestTracker   RequestTracker
+	Session          SessionProvider
+	AssertionHandler SamlAssertionHandler
 }
 
 // ServeHTTP implements http.Handler and serves the SAML-specific HTTP endpoints
@@ -92,6 +93,12 @@ func (m *Middleware) ServeACS(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	assertionErr := m.AssertionHandler.HandleAssertion(assertion)
+	if assertionErr != nil {
+		m.OnError(w, r, assertionErr)
+		return
+	}
+
 	m.CreateSessionFromAssertion(w, r, assertion, m.ServiceProvider.DefaultRedirectURI)
 	return
 }

samlsp/new.go

@@ -131,6 +131,12 @@ func DefaultServiceProvider(opts Options) saml.ServiceProvider {
 	}
 }
 
+// DefaultSamlAssertionHandler returns the default SamlAssertionHandler for the provided options,
+// a BasicSamlAssertionHandler configured to do nothing.
+func DefaultSamlAssertionHandler(opts Options) BasicSamlAssertionHandler {
+	return BasicSamlAssertionHandler{}
+}
+
 // New creates a new Middleware with the default providers for the
 // given options.
 //
@@ -139,11 +145,12 @@ func DefaultServiceProvider(opts Options) saml.ServiceProvider {
 // in the returned Middleware.
 func New(opts Options) (*Middleware, error) {
 	m := &Middleware{
-		ServiceProvider: DefaultServiceProvider(opts),
-		Binding:         "",
-		ResponseBinding: saml.HTTPPostBinding,
-		OnError:         DefaultOnError,
-		Session:         DefaultSessionProvider(opts),
+		ServiceProvider:  DefaultServiceProvider(opts),
+		Binding:          "",
+		ResponseBinding:  saml.HTTPPostBinding,
+		OnError:          DefaultOnError,
+		Session:          DefaultSessionProvider(opts),
+		AssertionHandler: DefaultSamlAssertionHandler(opts),
 	}
 	m.RequestTracker = DefaultRequestTracker(opts, &m.ServiceProvider)
 	if opts.UseArtifactResponse {

samlsp/saml_assertion_handler.go

@@ -0,0 +1,9 @@
+package samlsp
+
+import "github.com/crewjam/saml"
+
+// SamlAssertionHandler is an interface implemented by types that can handle
+// assertions and add extra functionality
+type SamlAssertionHandler interface {
+	HandleAssertion(assertion *saml.Assertion) error
+}