add --set-xauthrequest flag for use in Nginx auth_request mode

This is enhancement of #173 to use "Auth Request" consistently in
the command-line option, configuration file and response headers.
It always sets the X-Auth-Request-User response header and if the
email is available, sets X-Auth-Request-Email as well.

main.go

@@ -30,6 +30,7 @@ func main() {
 	flagSet.String("tls-cert", "", "path to certificate file")
 	flagSet.String("tls-key", "", "path to private key file")
 	flagSet.String("redirect-url", "", "the OAuth Redirect URL. ie: \"https://internalapp.yourcompany.com/oauth2/callback\"")
+	flagSet.Bool("set-xauthrequest", false, "set X-Auth-Request-User and X-Auth-Request-Email response headers (useful in Nginx auth_request mode)")
 	flagSet.Var(&upstreams, "upstream", "the http url(s) of the upstream endpoint or file:// paths for static files. Routing is based on the path")
 	flagSet.Bool("pass-basic-auth", true, "pass HTTP Basic Auth, X-Forwarded-User and X-Forwarded-Email information to upstream")
 	flagSet.Bool("pass-user-headers", true, "pass X-Forwarded-User and X-Forwarded-Email information to upstream")

oauthproxy.go

@@ -60,6 +60,7 @@ type OAuthProxy struct {
 	HtpasswdFile        *HtpasswdFile
 	DisplayHtpasswdForm bool
 	serveMux            http.Handler
+	SetXAuthRequest     bool
 	PassBasicAuth       bool
 	SkipProviderButton  bool
 	PassUserHeaders     bool
@@ -198,6 +199,7 @@ func NewOAuthProxy(opts *Options, validator func(string) bool) *OAuthProxy {
 		redirectURL:        redirectURL,
 		skipAuthRegex:      opts.SkipAuthRegex,
 		compiledRegex:      opts.CompiledRegex,
+		SetXAuthRequest:    opts.SetXAuthRequest,
 		PassBasicAuth:      opts.PassBasicAuth,
 		PassUserHeaders:    opts.PassUserHeaders,
 		BasicAuthPassword:  opts.BasicAuthPassword,
@@ -663,6 +665,12 @@ func (p *OAuthProxy) Authenticate(rw http.ResponseWriter, req *http.Request) int
 			req.Header["X-Forwarded-Email"] = []string{session.Email}
 		}
 	}
+	if p.SetXAuthRequest {
+		rw.Header().Set("X-Auth-Request-User", session.User)
+		if session.Email != "" {
+			rw.Header().Set("X-Auth-Request-Email", session.Email)
+		}
+	}
 	if p.PassAccessToken && session.AccessToken != "" {
 		req.Header["X-Forwarded-Access-Token"] = []string{session.AccessToken}
 	}

oauthproxy_test.go

@@ -611,6 +611,36 @@ func TestAuthOnlyEndpointUnauthorizedOnEmailValidationFailure(t *testing.T) {
 	assert.Equal(t, "unauthorized request\n", string(bodyBytes))
 }
 
+func TestAuthOnlyEndpointSetXAuthRequestHeaders(t *testing.T) {
+	var pc_test ProcessCookieTest
+
+	pc_test.opts = NewOptions()
+	pc_test.opts.SetXAuthRequest = true
+	pc_test.opts.Validate()
+
+	pc_test.proxy = NewOAuthProxy(pc_test.opts, func(email string) bool {
+		return pc_test.validate_user
+	})
+	pc_test.proxy.provider = &TestProvider{
+		ValidToken: true,
+	}
+
+	pc_test.validate_user = true
+
+	pc_test.rw = httptest.NewRecorder()
+	pc_test.req, _ = http.NewRequest("GET",
+		pc_test.opts.ProxyPrefix+"/auth", nil)
+
+	startSession := &providers.SessionState{
+		User: "oauth_user", Email: "oauth_user@example.com", AccessToken: "oauth_token"}
+	pc_test.SaveSession(startSession, time.Now())
+
+	pc_test.proxy.ServeHTTP(pc_test.rw, pc_test.req)
+	assert.Equal(t, http.StatusAccepted, pc_test.rw.Code)
+	assert.Equal(t, "oauth_user", pc_test.rw.HeaderMap["X-Auth-Request-User"][0])
+	assert.Equal(t, "oauth_user@example.com", pc_test.rw.HeaderMap["X-Auth-Request-Email"][0])
+}
+
 type SignatureAuthenticator struct {
 	auth hmacauth.HmacAuth
 }

options.go

@@ -57,6 +57,7 @@ type Options struct {
 	SkipProviderButton    bool     `flag:"skip-provider-button" cfg:"skip_provider_button"`
 	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"`
 
 	// These options allow for other providers besides Google, with
 	// potential overrides.
@@ -97,6 +98,7 @@ func NewOptions() *Options {
 		CookieHttpOnly:      true,
 		CookieExpire:        time.Duration(168) * time.Hour,
 		CookieRefresh:       time.Duration(0),
+		SetXAuthRequest:     false,
 		PassBasicAuth:       true,
 		PassUserHeaders:     true,
 		PassAccessToken:     false,