basicauth: Remove Authorization header on successful authz (issue #1324)

If a site owner protects a path with basicauth, no need
to use the Authorization header elsewhere upstream, especially since it
contains credentials.

If this breaks anyone, it means they're double-dipping. It's usually
good practice to clear out credentials as soon as they're not needed
anymore. (Note that we only clear credentials after they're used,
they stay for any other reason.)

caddyhttp/basicauth/basicauth.go

@@ -34,8 +34,7 @@ type BasicAuth struct {
 
 // ServeHTTP implements the httpserver.Handler interface.
 func (a BasicAuth) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
-	var hasAuth bool
-	var isAuthenticated bool
+	var protected, isAuthenticated bool
 
 	for _, rule := range a.Rules {
 		for _, res := range rule.Resources {
@@ -43,29 +42,33 @@ func (a BasicAuth) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error
 				continue
 			}
 
-			// Path matches; parse auth header
-			username, password, ok := r.BasicAuth()
-			hasAuth = true
+			// path matches; this endpoint is protected
+			protected = true
 
-			// Check credentials
+			// parse auth header
+			username, password, ok := r.BasicAuth()
+
+			// check credentials
 			if !ok ||
 				username != rule.Username ||
 				!rule.Password(password) {
 				continue
 			}
 
-			// Flag set only on successful authentication
+			// by this point, authentication was successful
 			isAuthenticated = true
+
+			// remove credentials from request to avoid leaking upstream
+			r.Header.Del("Authorization")
 		}
 	}
 
-	if hasAuth {
-		if !isAuthenticated {
-			w.Header().Set("WWW-Authenticate", "Basic realm=\"Restricted\"")
-			return http.StatusUnauthorized, nil
-		}
-		// "It's an older code, sir, but it checks out. I was about to clear them."
-		return a.Next.ServeHTTP(w, r)
+	if protected && !isAuthenticated {
+		// browsers show a message that says something like:
+		// "The website says: <realm>"
+		// which is kinda dumb, but whatever.
+		w.Header().Set("WWW-Authenticate", "Basic realm=\"Restricted\"")
+		return http.StatusUnauthorized, nil
 	}
 
 	// Pass-through when no paths match

caddyhttp/basicauth/basicauth_test.go

@@ -17,51 +17,57 @@ func TestBasicAuth(t *testing.T) {
 	rw := BasicAuth{
 		Next: httpserver.HandlerFunc(contentHandler),
 		Rules: []Rule{
-			{Username: "test", Password: PlainMatcher("ttest"), Resources: []string{"/testing"}},
+			{Username: "okuser", Password: PlainMatcher("okpass"), Resources: []string{"/testing"}},
 		},
 	}
 
 	tests := []struct {
-		from   string
-		result int
-		cred   string
+		from     string
+		result   int
+		user     string
+		password string
 	}{
-		{"/testing", http.StatusUnauthorized, "ttest:test"},
-		{"/testing", http.StatusOK, "test:ttest"},
-		{"/testing", http.StatusUnauthorized, ""},
+		{"/testing", http.StatusOK, "okuser", "okpass"},
+		{"/testing", http.StatusUnauthorized, "baduser", "okpass"},
+		{"/testing", http.StatusUnauthorized, "okuser", "badpass"},
+		{"/testing", http.StatusUnauthorized, "OKuser", "okpass"},
+		{"/testing", http.StatusUnauthorized, "OKuser", "badPASS"},
+		{"/testing", http.StatusUnauthorized, "", "okpass"},
+		{"/testing", http.StatusUnauthorized, "okuser", ""},
+		{"/testing", http.StatusUnauthorized, "", ""},
 	}
 
 	for i, test := range tests {
-
 		req, err := http.NewRequest("GET", test.from, nil)
 		if err != nil {
-			t.Fatalf("Test %d: Could not create HTTP request %v", i, err)
+			t.Fatalf("Test %d: Could not create HTTP request: %v", i, err)
 		}
-		auth := "Basic " + base64.StdEncoding.EncodeToString([]byte(test.cred))
-		req.Header.Set("Authorization", auth)
+		req.SetBasicAuth(test.user, test.password)
 
 		rec := httptest.NewRecorder()
 		result, err := rw.ServeHTTP(rec, req)
 		if err != nil {
-			t.Fatalf("Test %d: Could not ServeHTTP %v", i, err)
+			t.Fatalf("Test %d: Could not ServeHTTP: %v", i, err)
 		}
 		if result != test.result {
-			t.Errorf("Test %d: Expected Header '%d' but was '%d'",
+			t.Errorf("Test %d: Expected status code %d but was %d",
 				i, test.result, result)
 		}
-		if result == http.StatusUnauthorized {
+		if test.result == http.StatusUnauthorized {
 			headers := rec.Header()
 			if val, ok := headers["Www-Authenticate"]; ok {
-				if val[0] != "Basic realm=\"Restricted\"" {
-					t.Errorf("Test %d, Www-Authenticate should be %s provided %s", i, "Basic", val[0])
+				if got, want := val[0], "Basic realm=\"Restricted\""; got != want {
+					t.Errorf("Test %d: Www-Authenticate header should be '%s', got: '%s'", i, want, got)
 				}
 			} else {
-				t.Errorf("Test %d, should provide a header Www-Authenticate", i)
+				t.Errorf("Test %d: response should have a 'Www-Authenticate' header", i)
+			}
+		} else {
+			if got, want := req.Header.Get("Authorization"), ""; got != want {
+				t.Errorf("Test %d: Expected Authorization header to be stripped from request after successful authentication, but is: %s", i, got)
 			}
 		}
-
 	}
-
 }
 
 func TestMultipleOverlappingRules(t *testing.T) {