feat: add WWWAuthenticate field + Challenge(w) method to RequestAuthenticator

Co-authored-by: coolaj86 <122831+coolaj86@users.noreply.github.com>

auth/request.go

@@ -36,17 +36,32 @@ type RequestAuthenticator struct {
 	// TokenQueryParams lists query parameter names checked for tokens,
 	// e.g. []string{"access_token", "token"}.
 	TokenQueryParams []string
+
+	// WWWAuthenticate is the value sent in the WWW-Authenticate response header
+	// when Challenge is called. An empty string disables the header.
+	// NewRequestAuthenticator sets this to "Basic".
+	WWWAuthenticate string
 }
 
 // NewRequestAuthenticator returns a RequestAuthenticator with sane defaults:
 // Basic Auth enabled, Bearer/Token Authorization schemes, common API-key
-// headers, and access_token/token query params.
+// headers, access_token/token query params, and WWW-Authenticate: Basic.
 func NewRequestAuthenticator() *RequestAuthenticator {
 	return &RequestAuthenticator{
 		AuthenticateBasic:    true,
 		AuthorizationSchemes: []string{"Bearer", "Token"},
 		TokenHeaders:         []string{"X-API-Key", "X-Auth-Token", "X-Access-Token"},
 		TokenQueryParams:     []string{"access_token", "token"},
+		WWWAuthenticate:      "Basic",
+	}
+}
+
+// Challenge sets the WWW-Authenticate response header to ra.WWWAuthenticate
+// when it is non-empty. Call this before writing a 401 Unauthorized response
+// so that clients know which auth scheme to use.
+func (ra *RequestAuthenticator) Challenge(w http.ResponseWriter) {
+	if ra.WWWAuthenticate != "" {
+		w.Header().Set("WWW-Authenticate", ra.WWWAuthenticate)
 	}
 }
 

cmd/auth-proxy/main.go

@@ -76,6 +76,7 @@ type MainConfig struct {
 	ProxyTarget                string
 	AES128KeyPath              string
 	ShowVersion                bool
+	WWWAuthenticate            string
 	AuthorizationHeaderSchemes []string
 	TokenHeaderNames           []string
 	QueryParamNames            []string
@@ -84,6 +85,7 @@ type MainConfig struct {
 	tokenSchemeList            string
 	tokenHeaderList            string
 	tokenParamList             string
+	ra                         *auth.RequestAuthenticator
 }
 
 func (c *MainConfig) Addr() string {
@@ -102,6 +104,7 @@ func main() {
 		tokenSchemeList:            "",
 		tokenHeaderList:            "",
 		tokenParamList:             "",
+		WWWAuthenticate:            "Basic",
 		AuthorizationHeaderSchemes: nil, // []string{"Bearer", "Token"}
 		TokenHeaderNames:           nil, // []string{"X-API-Key", "X-Auth-Token", "X-Access-Token"},
 		QueryParamNames:            nil, // []string{"access_token", "token"},
@@ -282,6 +285,14 @@ func run(cli *MainConfig) {
 		log.Fatalf("Failed to load CSV auth: %v", err)
 	}
 
+	cli.ra = &auth.RequestAuthenticator{
+		Authenticator:        creds,
+		AuthorizationSchemes: cli.AuthorizationHeaderSchemes,
+		TokenHeaders:         cli.TokenHeaderNames,
+		TokenQueryParams:     cli.QueryParamNames,
+		WWWAuthenticate:      cli.WWWAuthenticate,
+	}
+
 	var usableRoles int
 	for key := range creds.CredentialKeys() {
 		u, err := creds.LoadCredential(key)
@@ -391,8 +402,7 @@ func (cli *MainConfig) newAuthProxyHandler(targetURL string) http.Handler {
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if !cli.authorize(r) {
-			// TODO allow --realm for `WWW-Authenticate: Basic realm="My Application"`
-			w.Header().Set("WWW-Authenticate", `Basic`)
+			cli.ra.Challenge(w)
 			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
@@ -593,13 +603,7 @@ func matchPattern(grant, rMethod, rHost, rPath string) bool {
 }
 
 func (cli *MainConfig) authenticate(r *http.Request) (auth.BasicPrinciple, error) {
-	ra := auth.RequestAuthenticator{
-		Authenticator:        creds,
-		AuthorizationSchemes: cli.AuthorizationHeaderSchemes,
-		TokenHeaders:         cli.TokenHeaderNames,
-		TokenQueryParams:     cli.QueryParamNames,
-	}
-	cred, err := ra.Authenticate(r)
+	cred, err := cli.ra.Authenticate(r)
 	if errors.Is(err, auth.ErrNoCredentials) {
 		return nil, ErrNoAuth
 	}

cmd/smsapid/main.go

@@ -39,6 +39,7 @@ var smsRequestAuth = &auth.RequestAuthenticator{
 	AuthenticateBasic:    true,
 	AuthorizationSchemes: []string{"*"},
 	TokenHeaders:         []string{"API-Key", "X-API-Key"},
+	WWWAuthenticate:      "Basic",
 }
 
 func main() {
@@ -145,13 +146,13 @@ func requireSMSPermission(permission string) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			if smsAuth == nil {
-				w.Header().Set("WWW-Authenticate", `Basic`)
+				smsRequestAuth.Challenge(w)
 				http.Error(w, "Unauthorized", http.StatusUnauthorized)
 				return
 			}
 			cred, err := smsRequestAuth.Authenticate(r)
 			if err != nil || !hasSMSPermission(cred.Permissions(), permission) {
-				w.Header().Set("WWW-Authenticate", `Basic`)
+				smsRequestAuth.Challenge(w)
 				http.Error(w, "Unauthorized", http.StatusUnauthorized)
 				return
 			}