fix: respect skip-auth-preflight in forward auth mode via X-Forwarded-Method

Signed-off-by: Kevin Stiehl <kevin.stiehl@maybit.email>

oauthproxy.go

@@ -587,7 +587,7 @@ func (p *OAuthProxy) ErrorPage(rw http.ResponseWriter, req *http.Request, code i
 
 // IsAllowedRequest is used to check if auth should be skipped for this request
 func (p *OAuthProxy) IsAllowedRequest(req *http.Request) bool {
-	isPreflightRequestAllowed := p.skipAuthPreflight && req.Method == http.MethodOptions
+	isPreflightRequestAllowed := p.skipAuthPreflight && requestutil.GetRequestMethod(req) == http.MethodOptions
 	return isPreflightRequestAllowed || p.isAllowedRoute(req) || p.isTrustedIP(req)
 }
 

pkg/requests/util/util.go

@@ -9,9 +9,10 @@ import (
 )
 
 const (
-	XForwardedProto = "X-Forwarded-Proto"
+	XForwardedProto  = "X-Forwarded-Proto"
-	XForwardedHost  = "X-Forwarded-Host"
+	XForwardedHost   = "X-Forwarded-Host"
-	XForwardedURI   = "X-Forwarded-Uri"
+	XForwardedURI    = "X-Forwarded-Uri"
+	XForwardedMethod = "X-Forwarded-Method"
 )
 
 // GetRequestProto returns the request scheme or X-Forwarded-Proto if present
@@ -45,6 +46,16 @@ func GetRequestURI(req *http.Request) string {
 	return uri
 }
 
+// GetRequestMethod returns the request method or X-Forwarded-Method if present
+// and the request came from a trusted reverse proxy.
+func GetRequestMethod(req *http.Request) string {
+	method := req.Header.Get(XForwardedMethod)
+	if !CanTrustForwardedHeaders(req) || method == "" {
+		return req.Method
+	}
+	return method
+}
+
 // GetRequestPath returns the request URI or X-Forwarded-Uri if present and the
 // request came from a trusted reverse proxy but always strips the query
 // parameters and fragment suffixes and only returns the pure path.

pkg/requests/util/util_test.go

@@ -200,6 +200,42 @@ var _ = Describe("Util Suite", func() {
 		})
 	})
 
+	Context("GetRequestMethod", func() {
+		Context("trusted forwarded headers are disabled", func() {
+			BeforeEach(func() {
+				req = middleware.AddRequestScope(req, &middleware.RequestScope{})
+			})
+
+			It("returns the request method", func() {
+				Expect(util.GetRequestMethod(req)).To(Equal(http.MethodGet))
+			})
+
+			It("ignores X-Forwarded-Method and returns the request method", func() {
+				req.Header.Add("X-Forwarded-Method", http.MethodOptions)
+				Expect(util.GetRequestMethod(req)).To(Equal(http.MethodGet))
+			})
+		})
+
+		Context("trusted forwarded headers are enabled", func() {
+			BeforeEach(func() {
+				req.RemoteAddr = "127.0.0.1:4180"
+				req = middleware.AddRequestScope(req, &middleware.RequestScope{
+					ReverseProxy:   true,
+					TrustedProxies: trustedProxies,
+				})
+			})
+
+			It("returns the request method if X-Forwarded-Method is not present", func() {
+				Expect(util.GetRequestMethod(req)).To(Equal(http.MethodGet))
+			})
+
+			It("returns the X-Forwarded-Method when present", func() {
+				req.Header.Add("X-Forwarded-Method", http.MethodOptions)
+				Expect(util.GetRequestMethod(req)).To(Equal(http.MethodOptions))
+			})
+		})
+	})
+
 	Context("CanTrustForwardedHeaders", func() {
 		It("returns false when no scope is present", func() {
 			Expect(util.CanTrustForwardedHeaders(req)).To(BeFalse())