fix: ensure canonical redirect URL is not empty

pkg/router/request/request.go

@@ -18,25 +18,35 @@ var (
 
 // CanonicalRedirectURL constructs a redirect URL that points back to the application.
 func CanonicalRedirectURL(r *http.Request) string {
+	// 1. default
 	redirectURL := "/"
 
+	// 2. Referer header is set
 	referer := RefererPath(r)
 	if len(referer) > 0 {
 		redirectURL = referer
 	}
 
+	// 3. redirect parameter is set
 	override := r.URL.Query().Get(RedirectURLParameter)
-	if len(override) > 0 {
-		referer, err := url.Parse(override)
-		if err == nil {
-			// strip scheme and host to avoid cross-domain redirects
-			referer.Scheme = ""
-			referer.Host = ""
-			redirectURL = referer.String()
-		}
+	if len(override) <= 0 {
+		return redirectURL
 	}
 
-	return redirectURL
+	overrideUrl, err := url.Parse(override)
+	if err != nil {
+		return redirectURL
+	}
+
+	// strip scheme and host to avoid cross-domain redirects
+	overrideUrl.Scheme = ""
+	overrideUrl.Host = ""
+	overrideString := overrideUrl.String()
+	if len(overrideString) <= 0 {
+		return "/"
+	}
+
+	return overrideString
 }
 
 // LoginURLParameter attempts to get a given parameter from the given HTTP request, falling back if none found.

pkg/router/request/request_test.go

@@ -23,10 +23,47 @@ func TestCanonicalRedirectURL(t *testing.T) {
 	assert.Equal(t, "/foo/bar/baz", request.CanonicalRedirectURL(r))
 
 	// If redirect parameter is set, use that
-	v := &url.Values{}
-	v.Set("redirect", "https://google.com/path/to/redirect?val1=foo&val2=bar")
-	r.URL.RawQuery = v.Encode()
-	assert.Equal(t, "/path/to/redirect?val1=foo&val2=bar", request.CanonicalRedirectURL(r))
+	t.Run("redirect parameter", func(t *testing.T) {
+		for _, test := range []struct {
+			name     string
+			value    string
+			expected string
+		}{
+			{
+				name:     "complete url with parameters",
+				value:    "https://google.com/path/to/redirect?val1=foo&val2=bar",
+				expected: "/path/to/redirect?val1=foo&val2=bar",
+			},
+			{
+				name:     "root url with trailing slash",
+				value:    "https://google.com/",
+				expected: "/",
+			},
+			{
+				name:     "root url without trailing slash",
+				value:    "https://google.com",
+				expected: "/",
+			},
+			{
+				name:     "url path with trailing slash",
+				value:    "https://google.com/path/",
+				expected: "/path/",
+			},
+			{
+				name:     "url path without trailing slash",
+				value:    "https://google.com/path",
+				expected: "/path",
+			},
+		} {
+			t.Run(test.name, func(t *testing.T) {
+				v := &url.Values{}
+				v.Set("redirect", test.value)
+				r.URL.RawQuery = v.Encode()
+				assert.Equal(t, test.expected, request.CanonicalRedirectURL(r))
+			})
+		}
+	})
+
 }
 
 func TestLoginURLParameter(t *testing.T) {