Add /auth endpoint to support Nginx's auth_request

Closes #152.

README.md

@@ -249,6 +249,7 @@ OAuth2 Proxy responds directly to the following endpoints. All other endpoints w
 * /oauth2/sign_in - the login page, which also doubles as a sign out page (it clears cookies)
 * /oauth2/start - a URL that will redirect to start the OAuth cycle
 * /oauth2/callback - the URL used at the end of the OAuth cycle. The oauth app will be configured with this as the callback url.
+* /oauth2/auth - only returns a 202 Accepted response or a 401 Unauthorized response; for use with the [Nginx `auth_request` directive](http://nginx.org/en/docs/http/ngx_http_auth_request_module.html)
 
 ## Logging Format
 

oauthproxy.go

@@ -33,6 +33,7 @@ type OAuthProxy struct {
 	SignInPath        string
 	OAuthStartPath    string
 	OAuthCallbackPath string
+	AuthOnlyPath      string
 
 	redirectURL         *url.URL // the url to receive requests at
 	provider            providers.Provider
@@ -156,6 +157,7 @@ func NewOAuthProxy(opts *Options, validator func(string) bool) *OAuthProxy {
 		SignInPath:        fmt.Sprintf("%s/sign_in", opts.ProxyPrefix),
 		OAuthStartPath:    fmt.Sprintf("%s/start", opts.ProxyPrefix),
 		OAuthCallbackPath: fmt.Sprintf("%s/callback", opts.ProxyPrefix),
+		AuthOnlyPath:      fmt.Sprintf("%s/auth", opts.ProxyPrefix),
 
 		ProxyPrefix:       opts.ProxyPrefix,
 		provider:          opts.provider,
@@ -390,6 +392,8 @@ func (p *OAuthProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		p.OAuthStart(rw, req)
 	case path == p.OAuthCallbackPath:
 		p.OAuthCallback(rw, req)
+	case path == p.AuthOnlyPath:
+		p.AuthenticateOnly(rw, req)
 	default:
 		p.Proxy(rw, req)
 	}
@@ -465,6 +469,21 @@ func (p *OAuthProxy) OAuthCallback(rw http.ResponseWriter, req *http.Request) {
 	}
 }
 
+func (p *OAuthProxy) AuthenticateOnly(rw http.ResponseWriter, req *http.Request) {
+	remoteAddr := getRemoteAddr(req)
+	if session, _, err := p.LoadCookiedSession(req); err != nil {
+		log.Printf("%s %s", remoteAddr, err)
+	} else if session.IsExpired() {
+		log.Printf("%s Expired", remoteAddr, session)
+	} else if !p.Validator(session.Email) {
+		log.Printf("%s Permission Denied", remoteAddr, session)
+	} else {
+		rw.WriteHeader(http.StatusAccepted)
+		return
+	}
+	http.Error(rw, "unauthorized request", http.StatusUnauthorized)
+}
+
 func (p *OAuthProxy) Proxy(rw http.ResponseWriter, req *http.Request) {
 	var saveSession, clearSession, revalidated bool
 	remoteAddr := getRemoteAddr(req)

oauthproxy_test.go

@@ -555,3 +555,58 @@ func TestProcessCookieFailIfRefreshSetAndCookieExpired(t *testing.T) {
 		t.Errorf("expected nil session %#v", session)
 	}
 }
+
+func NewAuthOnlyEndpointTest() *ProcessCookieTest {
+	pc_test := NewProcessCookieTestWithDefaults()
+	pc_test.req, _ = http.NewRequest("GET",
+		pc_test.opts.ProxyPrefix + "/auth", nil)
+	return pc_test
+}
+
+func TestAuthOnlyEndpointAccepted(t *testing.T) {
+	test := NewAuthOnlyEndpointTest()
+	startSession := &providers.SessionState{
+		Email: "michael.bland@gsa.gov", AccessToken: "my_access_token"}
+	test.SaveSession(startSession, time.Now())
+
+	test.proxy.ServeHTTP(test.rw, test.req)
+	assert.Equal(t, http.StatusAccepted, test.rw.Code)
+	bodyBytes, _ := ioutil.ReadAll(test.rw.Body)
+	assert.Equal(t, "", string(bodyBytes))
+}
+
+func TestAuthOnlyEndpointUnauthorizedOnNoCookieSetError(t *testing.T) {
+	test := NewAuthOnlyEndpointTest()
+
+	test.proxy.ServeHTTP(test.rw, test.req)
+	assert.Equal(t, http.StatusUnauthorized, test.rw.Code)
+	bodyBytes, _ := ioutil.ReadAll(test.rw.Body)
+	assert.Equal(t, "unauthorized request\n", string(bodyBytes))
+}
+
+func TestAuthOnlyEndpointUnauthorizedOnExpiration(t *testing.T) {
+	test := NewAuthOnlyEndpointTest()
+	test.proxy.CookieExpire = time.Duration(24) * time.Hour
+	reference := time.Now().Add(time.Duration(25) * time.Hour * -1)
+	startSession := &providers.SessionState{
+		Email: "michael.bland@gsa.gov", AccessToken: "my_access_token"}
+	test.SaveSession(startSession, reference)
+
+	test.proxy.ServeHTTP(test.rw, test.req)
+	assert.Equal(t, http.StatusUnauthorized, test.rw.Code)
+	bodyBytes, _ := ioutil.ReadAll(test.rw.Body)
+	assert.Equal(t, "unauthorized request\n", string(bodyBytes))
+}
+
+func TestAuthOnlyEndpointUnauthorizedOnEmailValidationFailure(t *testing.T) {
+	test := NewAuthOnlyEndpointTest()
+	startSession := &providers.SessionState{
+		Email: "michael.bland@gsa.gov", AccessToken: "my_access_token"}
+	test.SaveSession(startSession, time.Now())
+	test.validate_user = false
+
+	test.proxy.ServeHTTP(test.rw, test.req)
+	assert.Equal(t, http.StatusUnauthorized, test.rw.Code)
+	bodyBytes, _ := ioutil.ReadAll(test.rw.Body)
+	assert.Equal(t, "unauthorized request\n", string(bodyBytes))
+}