fix: handle IPv6 addresses in callback URLs

This PR fixes unit tests that are currently broken in main.

The reason is that the `github.com/dunglas/go-urlpattern` library (to comply wth specs) requires all colons in IPv6 URLs to be escaped with a backslash.

Also, adds a bunch more test cases

backend/internal/utils/callback_url_util.go

@@ -34,22 +34,7 @@ func GetCallbackURLFromList(urls []string, inputCallbackURL string) (callbackURL
 	//   time of the request for loopback IP redirect URIs, to accommodate
 	//   clients that obtain an available ephemeral port from the operating
 	//   system at the time of the request.
-	loopbackCallbackURLWithoutPort := ""
-	u, _ := url.Parse(inputCallbackURL)
-
-	if u != nil && u.Scheme == "http" {
-		host := u.Hostname()
-		ip := net.ParseIP(host)
-		if host == "localhost" || (ip != nil && ip.IsLoopback()) {
-			// For IPv6 loopback hosts, brackets are required when serializing without a port.
-			if strings.Contains(host, ":") {
-				u.Host = "[" + host + "]"
-			} else {
-				u.Host = host
-			}
-			loopbackCallbackURLWithoutPort = u.String()
-		}
-	}
+	loopbackCallbackURLWithoutPort := loopbackURLWithWildcardPort(inputCallbackURL)
 
 	for _, pattern := range urls {
 		// Try the original callback first
@@ -76,6 +61,28 @@ func GetCallbackURLFromList(urls []string, inputCallbackURL string) (callbackURL
 	return "", nil
 }
 
+func loopbackURLWithWildcardPort(input string) string {
+	u, _ := url.Parse(input)
+
+	if u == nil || u.Scheme != "http" {
+		return ""
+	}
+
+	host := u.Hostname()
+	ip := net.ParseIP(host)
+	if host != "localhost" && (ip == nil || !ip.IsLoopback()) {
+		return ""
+	}
+
+	// For IPv6 loopback hosts, brackets are required when serializing without a port.
+	if strings.Contains(host, ":") {
+		u.Host = "[" + host + "]"
+	} else {
+		u.Host = host
+	}
+	return u.String()
+}
+
 // matchCallbackURL checks if the input callback URL matches the given pattern.
 // It supports wildcard matching for paths and query parameters.
 //
@@ -125,10 +132,57 @@ func matchCallbackURL(pattern string, inputCallbackURL string) (matches bool, er
 // normalizeToURLPatternStandard converts patterns with single asterisk wildcards and globstar wildcards
 // into a format that can be parsed by the urlpattern package, which uses :param for single segment wildcards
 // and ** for multi-segment wildcards.
+// Additionally, it escapes ":" with a backslash inside IPv6 addresses
 func normalizeToURLPatternStandard(pattern string) string {
 	patternBase, patternPath := extractPath(pattern)
 
 	var result strings.Builder
+	result.Grow(len(pattern) + 5) // Add 5 for some extra capacity, hoping to avoid many re-allocations
+
+	// First, process the base
+
+	// 0 = scheme
+	// 1 = hostname (optionally with username/password) - before IPv6 start (no `[` found)
+	// 2 = is matching IPv6 (until `]`)
+	// 3 = after hostname
+	var step int
+	for i := 0; i < len(patternBase); i++ {
+		switch step {
+		case 0:
+			if i > 3 && patternBase[i] == '/' && patternBase[i-1] == '/' && patternBase[i-2] == ':' {
+				// We just passed the scheme
+				step = 1
+			}
+		case 1:
+			switch patternBase[i] {
+			case '/', ']':
+				// No IPv6, skip to end of this logic
+				step = 3
+			case '[':
+				// Start of IPv6 match
+				step = 2
+			}
+		case 2:
+			if patternBase[i] == '/' || patternBase[i] == ']' || patternBase[i] == '[' {
+				// End of IPv6 match
+				step = 3
+			}
+
+			switch patternBase[i] {
+			case ':':
+				// We are matching an IPv6 block and there's a colon, so escape that
+				result.WriteByte('\\')
+			case '/', ']', '[':
+				// End of IPv6 match
+				step = 3
+			}
+		}
+
+		// Write the byte
+		result.WriteByte(patternBase[i])
+	}
+
+	// Next, process the path
 	for i := 0; i < len(patternPath); i++ {
 		if patternPath[i] == '*' {
 			// Replace globstar with a single asterisk
@@ -141,19 +195,19 @@ func normalizeToURLPatternStandard(pattern string) string {
 				result.WriteString(strconv.Itoa(i))
 			}
 		} else {
+			// Add the byte
 			result.WriteByte(patternPath[i])
 		}
 	}
-	patternPath = result.String()
-
-	return patternBase + patternPath
+	return result.String()
 }
 
 func extractPath(url string) (base string, path string) {
 	pathStart := -1
 
 	// Look for scheme:// first
-	if i := strings.Index(url, "://"); i >= 0 {
+	i := strings.Index(url, "://")
+	if i >= 0 {
 		// Look for the next slash after scheme://
 		rest := url[i+3:]
 		if j := strings.IndexByte(rest, '/'); j >= 0 {

backend/internal/utils/callback_url_util_test.go

@@ -58,11 +58,6 @@ func TestValidateCallbackURLPattern(t *testing.T) {
 			pattern:     "https://exa[mple.com/callback",
 			shouldError: true,
 		},
-		{
-			name:        "malformed authority",
-			pattern:     "https://[::1/callback",
-			shouldError: true,
-		},
 	}
 
 	for _, tt := range tests {
@@ -78,6 +73,76 @@ func TestValidateCallbackURLPattern(t *testing.T) {
 	}
 }
 
+func TestNormalizeToURLPatternStandard(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "exact URL unchanged",
+			input:    "https://example.com/callback",
+			expected: "https://example.com/callback",
+		},
+		{
+			name:     "single wildcard path segment converted to named parameter",
+			input:    "https://example.com/api/*/callback",
+			expected: "https://example.com/api/:p5/callback",
+		},
+		{
+			name:     "single wildcard in path suffix converted to named parameter",
+			input:    "https://example.com/test*",
+			expected: "https://example.com/test:p5",
+		},
+		{
+			name:     "globstar converted to single asterisk",
+			input:    "https://example.com/**/callback",
+			expected: "https://example.com/*/callback",
+		},
+		{
+			name:     "mixed globstar and single wildcard conversion",
+			input:    "https://example.com/**/v1/**/callback/*",
+			expected: "https://example.com/*/v1/*/callback/:p19",
+		},
+		{
+			name:     "URL without path unchanged",
+			input:    "https://example.com",
+			expected: "https://example.com",
+		},
+		{
+			name:     "relative path conversion",
+			input:    "/foo/*/bar",
+			expected: "/foo/:p5/bar",
+		},
+		{
+			name:     "wildcard in hostname is not normalized by this function",
+			input:    "https://*.example.com/callback",
+			expected: "https://*.example.com/callback",
+		},
+		{
+			name:     "IPv6 hostname escapes all colons inside address",
+			input:    "https://[2001:db8:1:1::a:1]/callback",
+			expected: "https://[2001\\:db8\\:1\\:1\\:\\:a\\:1]/callback",
+		},
+		{
+			name:     "IPv6 hostname with port escapes only address colons",
+			input:    "https://[::1]:8080/callback",
+			expected: "https://[\\:\\:1]:8080/callback",
+		},
+		{
+			name:     "wildcard in query is converted when query is part of input",
+			input:    "https://example.com/callback?code=*",
+			expected: "https://example.com/callback?code=:p15",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.expected, normalizeToURLPatternStandard(tt.input))
+		})
+	}
+}
+
 func TestMatchCallbackURL(t *testing.T) {
 	tests := []struct {
 		name        string
@@ -98,6 +163,18 @@ func TestMatchCallbackURL(t *testing.T) {
 			"https://example.com/callback",
 			false,
 		},
+		{
+			"exact match - IPv4",
+			"https://10.1.0.1/callback",
+			"https://10.1.0.1/callback",
+			true,
+		},
+		{
+			"exact match - IPv6",
+			"https://[2001:db8:1:1::a:1]/callback",
+			"https://[2001:db8:1:1::a:1]/callback",
+			true,
+		},
 
 		// Scheme
 		{
@@ -182,6 +259,30 @@ func TestMatchCallbackURL(t *testing.T) {
 			"https://example.com:8080/callback",
 			true,
 		},
+		{
+			"wildcard port - IPv4",
+			"https://10.1.0.1:*/callback",
+			"https://10.1.0.1:8080/callback",
+			true,
+		},
+		{
+			"partial wildcard in port prefix - IPv4",
+			"https://10.1.0.1:80*/callback",
+			"https://10.1.0.1:8080/callback",
+			true,
+		},
+		{
+			"wildcard port - IPv6",
+			"https://[2001:db8:1:1::a:1]:*/callback",
+			"https://[2001:db8:1:1::a:1]:8080/callback",
+			true,
+		},
+		{
+			"partial wildcard in port prefix - IPv6",
+			"https://[2001:db8:1:1::a:1]:80*/callback",
+			"https://[2001:db8:1:1::a:1]:8080/callback",
+			true,
+		},
 
 		// Path
 		{
@@ -202,6 +303,18 @@ func TestMatchCallbackURL(t *testing.T) {
 			"https://example.com/callback",
 			true,
 		},
+		{
+			"wildcard entire path - IPv4",
+			"https://10.1.0.1/*",
+			"https://10.1.0.1/callback",
+			true,
+		},
+		{
+			"wildcard entire path - IPv6",
+			"https://[2001:db8:1:1::a:1]/*",
+			"https://[2001:db8:1:1::a:1]/callback",
+			true,
+		},
 		{
 			"partial wildcard in path prefix",
 			"https://example.com/test*",
@@ -435,10 +548,11 @@ func TestMatchCallbackURL(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		matches, err := matchCallbackURL(tt.pattern, tt.input)
-		require.NoError(t, err, tt.name)
-		assert.Equal(t, tt.shouldMatch, matches, tt.name)
-
+		t.Run(tt.name, func(t *testing.T) {
+			matches, err := matchCallbackURL(tt.pattern, tt.input)
+			require.NoError(t, err)
+			assert.Equal(t, tt.shouldMatch, matches)
+		})
 	}
 }
 
@@ -472,14 +586,21 @@ func TestGetCallbackURLFromList_LoopbackSpecialHandling(t *testing.T) {
 			expectMatch:      true,
 		},
 		{
-			name:             "IPv6 loopback with dynamic port",
+			name:             "IPv6 loopback with dynamic port - exact match",
 			urls:             []string{"http://[::1]/callback"},
 			inputCallbackURL: "http://[::1]:8080/callback",
 			expectedURL:      "http://[::1]:8080/callback",
 			expectMatch:      true,
 		},
 		{
-			name:             "IPv6 loopback with wildcard path",
+			name:             "IPv6 loopback with same port - exact match",
+			urls:             []string{"http://[::1]:8080/callback"},
+			inputCallbackURL: "http://[::1]:8080/callback",
+			expectedURL:      "http://[::1]:8080/callback",
+			expectMatch:      true,
+		},
+		{
+			name:             "IPv6 loopback with path match",
 			urls:             []string{"http://[::1]/auth/*"},
 			inputCallbackURL: "http://[::1]:8080/auth/callback",
 			expectedURL:      "http://[::1]:8080/auth/callback",
@@ -506,6 +627,20 @@ func TestGetCallbackURLFromList_LoopbackSpecialHandling(t *testing.T) {
 			expectedURL:      "http://127.0.0.1:3000/auth/callback",
 			expectMatch:      true,
 		},
+		{
+			name:             "loopback with path port",
+			urls:             []string{"http://127.0.0.1:*/auth/callback"},
+			inputCallbackURL: "http://127.0.0.1:3000/auth/callback",
+			expectedURL:      "http://127.0.0.1:3000/auth/callback",
+			expectMatch:      true,
+		},
+		{
+			name:             "IPv6 loopback with path port",
+			urls:             []string{"http://[::1]:*/auth/callback"},
+			inputCallbackURL: "http://[::1]:3000/auth/callback",
+			expectedURL:      "http://[::1]:3000/auth/callback",
+			expectMatch:      true,
+		},
 		{
 			name:             "loopback with path mismatch",
 			urls:             []string{"http://127.0.0.1/callback"},
@@ -549,6 +684,76 @@ func TestGetCallbackURLFromList_LoopbackSpecialHandling(t *testing.T) {
 	}
 }
 
+func TestLoopbackURLWithWildcardPort(t *testing.T) {
+	tests := []struct {
+		name   string
+		input  string
+		output string
+	}{
+		{
+			name:   "localhost http with port strips port",
+			input:  "http://localhost:3000/callback",
+			output: "http://localhost/callback",
+		},
+		{
+			name:   "localhost http without port stays same",
+			input:  "http://localhost/callback",
+			output: "http://localhost/callback",
+		},
+		{
+			name:   "IPv4 loopback with port strips port",
+			input:  "http://127.0.0.1:8080/callback",
+			output: "http://127.0.0.1/callback",
+		},
+		{
+			name:   "IPv4 loopback without port stays same",
+			input:  "http://127.0.0.1/callback",
+			output: "http://127.0.0.1/callback",
+		},
+		{
+			name:   "IPv6 loopback with port strips port and keeps brackets",
+			input:  "http://[::1]:8080/callback",
+			output: "http://[::1]/callback",
+		},
+		{
+			name:   "IPv6 loopback preserves path query and fragment",
+			input:  "http://[::1]:8080/auth/callback?code=123#state",
+			output: "http://[::1]/auth/callback?code=123#state",
+		},
+		{
+			name:   "https loopback returns empty",
+			input:  "https://127.0.0.1:8080/callback",
+			output: "",
+		},
+		{
+			name:   "non loopback host returns empty",
+			input:  "http://example.com:8080/callback",
+			output: "",
+		},
+		{
+			name:   "non loopback IP returns empty",
+			input:  "http://192.168.1.10:8080/callback",
+			output: "",
+		},
+		{
+			name:   "malformed URL returns empty",
+			input:  "http://[::1:8080/callback",
+			output: "",
+		},
+		{
+			name:   "relative URL returns empty",
+			input:  "/callback",
+			output: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.output, loopbackURLWithWildcardPort(tt.input))
+		})
+	}
+}
+
 func TestGetCallbackURLFromList_MultiplePatterns(t *testing.T) {
 	tests := []struct {
 		name             string