Added support for a static RelayState value

README.md

@@ -49,6 +49,9 @@ Provides a SAML SP authentication proxy for backend web services
         The path to the X509 public certificate PEM file for this SP (env SAML_PROXY_SP_CERT_PATH) (default "saml-auth-proxy.cert")
   -sp-key-path path
         The path to the X509 private key PEM file for this SP (env SAML_PROXY_SP_KEY_PATH) (default "saml-auth-proxy.key")
+  -static-relay-state string
+        A fixed RelayState value, such as a short URL. Will be trimmed to 80 characters to conform with SAML. The default generates random bytes that are Base64
+ encoded. (env SAML_PROXY_STATIC_RELAY_STATE)
   -version
         show version and exit
 ```

server/config.go

@@ -24,4 +24,5 @@ type Config struct {
 	AllowIdpInitiated       bool              `usage:"If set, allows for IdP initiated authentication flow"`
 	AuthVerifyPath          string            `default:"/_verify" usage:"Path under BaseUrl that will respond with a 200 when authenticated"`
 	Debug                   bool              `usage:"Enable debug logs"`
+	StaticRelayState        string            `usage:"A fixed RelayState value, such as a short URL. Will be trimmed to 80 characters to conform with SAML. The default generates random bytes that are Base64 encoded."`
 }

server/request_tracker_cookie.go

@@ -13,7 +13,16 @@ import (
 type CookieRequestTracker struct {
 	samlsp.CookieRequestTracker
 
-	CookieDomain string
+	CookieDomain     string
+	StaticRelayState string
+}
+
+func minOfInts(x, y int) int {
+	if x < y {
+		return x
+	} else {
+		return y
+	}
 }
 
 // Source: https://github.com/crewjam/saml/blob/5e0ffd290abf0be7dfd4f8279e03a963071544eb/samlsp/request_tracker_cookie.go#L28-58
@@ -28,7 +37,9 @@ func (t CookieRequestTracker) TrackRequest(w http.ResponseWriter, r *http.Reques
 		URI:           r.URL.String(),
 	}
 
-	if t.RelayStateFunc != nil {
+	if t.StaticRelayState != "" {
+		trackedRequest.Index = t.StaticRelayState[0:minOfInts(80, len(t.StaticRelayState))]
+	} else if t.RelayStateFunc != nil {
 		relayState := t.RelayStateFunc(w, r)
 		if relayState != "" {
 			trackedRequest.Index = relayState

server/server.go

@@ -85,7 +85,8 @@ func Start(ctx context.Context, logger *zap.Logger, cfg *Config) error {
 			URL: *rootUrl,
 			Key: keyPair.PrivateKey.(*rsa.PrivateKey),
 		}, &middleware.ServiceProvider),
-		CookieDomain: cookieDomain,
+		CookieDomain:     cookieDomain,
+		StaticRelayState: cfg.StaticRelayState,
 	}
 	cookieSessionProvider := samlsp.DefaultSessionProvider(samlOpts)
 	cookieSessionProvider.Name = cfg.CookieName