#369: Optionally allow skipping authentication for preflight requests

README.md

@@ -199,6 +199,7 @@ Usage of oauth2_proxy:
   -scope="": Oauth scope specification
   -signature-key="": GAP-Signature request signature key (algorithm:secretkey)
   -skip-auth-regex=: bypass authentication for requests path's that match (may be given multiple times)
+  -skip-auth-preflight=false: bypass authentication for OPTIONAL requests so preflight requests could succeed when using CORS
   -skip-provider-button=false: will skip sign-in-page to directly reach the next step: oauth/start
   -ssl-insecure-skip-verify: skip validation of certificates presented when using HTTPS
   -tls-cert="": path to certificate file

main.go

@@ -39,6 +39,7 @@ func main() {
 	flagSet.Bool("pass-host-header", true, "pass the request Host Header to upstream")
 	flagSet.Var(&skipAuthRegex, "skip-auth-regex", "bypass authentication for requests path's that match (may be given multiple times)")
 	flagSet.Bool("skip-provider-button", false, "will skip sign-in-page to directly reach the next step: oauth/start")
+	flagSet.Bool("skip-auth-preflight", false, "will skip authentication for OPTIONS requests")
 	flagSet.Bool("ssl-insecure-skip-verify", false, "skip validation of certificates presented when using HTTPS")
 
 	flagSet.Var(&emailDomains, "email-domain", "authenticate emails with the specified domain (may be given multiple times). Use * to authenticate any email")

oauthproxy.go

@@ -68,6 +68,7 @@ type OAuthProxy struct {
 	PassAccessToken     bool
 	CookieCipher        *cookie.Cipher
 	skipAuthRegex       []string
+	skipAuthPreflight   bool
 	compiledRegex       []*regexp.Regexp
 	templates           *template.Template
 	Footer              string
@@ -198,6 +199,7 @@ func NewOAuthProxy(opts *Options, validator func(string) bool) *OAuthProxy {
 		serveMux:           serveMux,
 		redirectURL:        redirectURL,
 		skipAuthRegex:      opts.SkipAuthRegex,
+		skipAuthPreflight:  opts.SkipAuthPreflight,
 		compiledRegex:      opts.CompiledRegex,
 		SetXAuthRequest:    opts.SetXAuthRequest,
 		PassBasicAuth:      opts.PassBasicAuth,
@@ -421,6 +423,11 @@ func (p *OAuthProxy) GetRedirect(req *http.Request) (redirect string, err error)
 	return
 }
 
+func (p *OAuthProxy) IsWhitelistedRequest(req *http.Request) (ok bool) {
+	isPreflightRequestAllowed := p.skipAuthPreflight && req.Method == "OPTIONS"
+	return isPreflightRequestAllowed || p.IsWhitelistedPath(req.URL.Path)
+}
+
 func (p *OAuthProxy) IsWhitelistedPath(path string) (ok bool) {
 	for _, u := range p.compiledRegex {
 		ok = u.MatchString(path)
@@ -445,7 +452,7 @@ func (p *OAuthProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		p.RobotsTxt(rw)
 	case path == p.PingPath:
 		p.PingPage(rw)
-	case p.IsWhitelistedPath(path):
+	case p.IsWhitelistedRequest(req):
 		p.serveMux.ServeHTTP(rw, req)
 	case path == p.SignInPath:
 		p.SignIn(rw, req)

oauthproxy_test.go

@@ -641,6 +641,33 @@ func TestAuthOnlyEndpointSetXAuthRequestHeaders(t *testing.T) {
 	assert.Equal(t, "oauth_user@example.com", pc_test.rw.HeaderMap["X-Auth-Request-Email"][0])
 }
 
+func TestAuthSkippedForPreflightRequests(t *testing.T) {
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("response"))
+	}))
+	defer upstream.Close()
+
+	opts := NewOptions()
+	opts.Upstreams = append(opts.Upstreams, upstream.URL)
+	opts.ClientID = "bazquux"
+	opts.ClientSecret = "foobar"
+	opts.CookieSecret = "xyzzyplugh"
+	opts.SkipAuthPreflight = true
+	opts.Validate()
+
+	upstream_url, _ := url.Parse(upstream.URL)
+	opts.provider = NewTestProvider(upstream_url, "")
+
+	proxy := NewOAuthProxy(opts, func(string) bool { return false })
+	rw := httptest.NewRecorder()
+	req, _ := http.NewRequest("OPTIONS", "/preflight-request", nil)
+	proxy.ServeHTTP(rw, req)
+
+	assert.Equal(t, 200, rw.Code)
+	assert.Equal(t, "response", rw.Body.String())
+}
+
 type SignatureAuthenticator struct {
 	auth hmacauth.HmacAuth
 }

options.go

@@ -58,6 +58,7 @@ type Options struct {
 	PassUserHeaders       bool     `flag:"pass-user-headers" cfg:"pass_user_headers"`
 	SSLInsecureSkipVerify bool     `flag:"ssl-insecure-skip-verify" cfg:"ssl_insecure_skip_verify"`
 	SetXAuthRequest       bool     `flag:"set-xauthrequest" cfg:"set_xauthrequest"`
+	SkipAuthPreflight     bool     `flag:"skip-auth-preflight" cfg:"skip_auth_preflight"`
 
 	// These options allow for other providers besides Google, with
 	// potential overrides.
@@ -99,6 +100,7 @@ func NewOptions() *Options {
 		CookieExpire:        time.Duration(168) * time.Hour,
 		CookieRefresh:       time.Duration(0),
 		SetXAuthRequest:     false,
+		SkipAuthPreflight:   false,
 		PassBasicAuth:       true,
 		PassUserHeaders:     true,
 		PassAccessToken:     false,