form: allow relative redirect_url

EvaluateRelativePath will un-relative-ize a path if it is relative (has
a preceding /) in the same way as app.ExternalURI() roughly. Should fix #414.

config.go

@@ -47,6 +47,10 @@ func (app *appContext) MustSetURLPath(section, key, val string) {
 }
 
 func FixFullURL(v string) string {
+	// Keep relative paths relative
+	if strings.HasPrefix(v, "/") {
+		return v
+	}
 	if !strings.HasPrefix(v, "http://") && !strings.HasPrefix(v, "https://") {
 		v = "http://" + v
 	}
@@ -98,6 +102,21 @@ func (app *appContext) ExternalURI(gc *gin.Context) string {
 	return app.externalURI
 }
 
+func (app *appContext) EvaluateRelativePath(gc *gin.Context, path string) string {
+	if !strings.HasPrefix(path, "/") {
+		return path
+	}
+
+	var proto string
+	if gc.Request.TLS != nil || gc.Request.Header.Get("X-Forwarded-Proto") == "https" || gc.Request.Header.Get("X-Forwarded-Protocol") == "https" {
+		proto = "https://"
+	} else {
+		proto = "http://"
+	}
+
+	return proto + app.ExternalDomain(gc) + path
+}
+
 func (app *appContext) loadConfig() error {
 	var err error
 	app.config, err = ini.ShadowLoad(app.configPath)

views.go

@@ -236,7 +236,7 @@ func (app *appContext) MyUserPage(gc *gin.Context) {
 		"validationStrings": app.storage.lang.User[lang].validationStringsJSON,
 		"language":          app.storage.lang.User[lang].JSON,
 		"langName":          lang,
-		"jfLink":            app.config.Section("ui").Key("redirect_url").String(),
+		"jfLink":            app.EvaluateRelativePath(gc, app.config.Section("ui").Key("redirect_url").String()),
 		"requirements":      app.validator.getCriteria(),
 	}
 	if telegramEnabled {
@@ -305,7 +305,7 @@ func (app *appContext) ResetPassword(gc *gin.Context) {
 	if setPassword {
 		data["helpMessage"] = app.config.Section("ui").Key("help_message").String()
 		data["successMessage"] = app.config.Section("ui").Key("success_message").String()
-		data["jfLink"] = app.config.Section("ui").Key("redirect_url").String()
+		data["jfLink"] = app.EvaluateRelativePath(gc, app.config.Section("ui").Key("redirect_url").String())
 		data["redirectToJellyfin"] = app.config.Section("ui").Key("auto_redirect").MustBool(false)
 		data["validate"] = app.config.Section("password_validation").Key("enabled").MustBool(false)
 		data["requirements"] = app.validator.getCriteria()
@@ -688,7 +688,7 @@ func (app *appContext) NewUserFromConfirmationKey(invite Invite, key string, lan
 
 	app.PostNewUserFromInvite(nu, req, profile, invite)
 
-	jfLink := app.config.Section("ui").Key("redirect_url").String()
+	jfLink := app.EvaluateRelativePath(gc, app.config.Section("ui").Key("redirect_url").String())
 	if app.config.Section("ui").Key("auto_redirect").MustBool(false) {
 		gc.Redirect(301, jfLink)
 	} else {
@@ -756,7 +756,7 @@ func (app *appContext) InviteProxy(gc *gin.Context) {
 		"contactMessage":     app.config.Section("ui").Key("contact_message").String(),
 		"helpMessage":        app.config.Section("ui").Key("help_message").String(),
 		"successMessage":     app.config.Section("ui").Key("success_message").String(),
-		"jfLink":             app.config.Section("ui").Key("redirect_url").String(),
+		"jfLink":             app.EvaluateRelativePath(gc, app.config.Section("ui").Key("redirect_url").String()),
 		"redirectToJellyfin": app.config.Section("ui").Key("auto_redirect").MustBool(false),
 		"validate":           app.config.Section("password_validation").Key("enabled").MustBool(false),
 		"requirements":       app.validator.getCriteria(),