Support non-root prefixed reverse proxy environments (#45)

* support X-Forwarded-Prefix for reverse proxied prefix stripping environments

* sign cla

---------

Co-authored-by: Nick Gregory <nick.gregory@openenterprise.co.uk>
Co-authored-by: Paul Greenberg <greenpau@users.noreply.github.com>

assets/cla/consent.yaml

@@ -37,3 +37,5 @@
   email: sergiucozma1994@gmail.com
 - name: Riccardo Piola
   email: riccardopiola@live.it
+- name: Nick Gregory
+  email: ng-cla@openenterprise.co.uk

pkg/util/addr/utils.go

@@ -169,6 +169,10 @@ func GetCurrentURLWithSuffix(r *http.Request, suffix string) (string, error) {
 			u += ":" + port
 		}
 	}
+
+	prefix := r.Header.Get("X-Forwarded-Prefix")
+	u += prefix
+
 	if suffix != "" {
 		i := strings.Index(r.RequestURI, suffix)
 		if i < 0 {

pkg/util/redirect.go

@@ -96,6 +96,8 @@ func GetCurrentBaseURL(r *http.Request) string {
 			redirectBaseURL += ":" + redirPort
 		}
 	}
+	redirPrefix := r.Header.Get("X-Forwarded-Prefix")
+	redirectBaseURL += redirPrefix
 
 	return redirectBaseURL
 }