Redirect to / when /oauth2/sign_in accessed

Without this change, clicking the sign-in button on /oauth2/sign_in will
always redirect back to /oauth2/sign_in, essentially creating an infinite
loop.

oauthproxy.go

@@ -307,6 +307,11 @@ func (p *OauthProxy) SignInPage(rw http.ResponseWriter, req *http.Request, code
 	p.ClearCookie(rw, req)
 	rw.WriteHeader(code)
 
+	redirect_url := req.URL.RequestURI()
+	if redirect_url == signInPath {
+		redirect_url = "/"
+	}
+
 	t := struct {
 		ProviderName  string
 		SignInMessage string
@@ -317,7 +322,7 @@ func (p *OauthProxy) SignInPage(rw http.ResponseWriter, req *http.Request, code
 		ProviderName:  p.provider.Data().ProviderName,
 		SignInMessage: p.SignInMessage,
 		CustomLogin:   p.displayCustomLoginForm(),
-		Redirect:      req.URL.RequestURI(),
+		Redirect:      redirect_url,
 		Version:       VERSION,
 	}
 	p.templates.ExecuteTemplate(rw, "sign_in.html", t)

oauthproxy_test.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"regexp"
 	"strings"
 	"testing"
 	"time"
@@ -237,3 +238,69 @@ func TestDoNotForwardAccessTokenUpstream(t *testing.T) {
 	assert.Equal(t, 200, code)
 	assert.Equal(t, "No access token found.", payload)
 }
+
+type SignInPageTest struct {
+	opts           *Options
+	proxy          *OauthProxy
+	sign_in_regexp *regexp.Regexp
+}
+
+const signInRedirectPattern = `<input type="hidden" name="rd" value="(.*)">`
+
+func NewSignInPageTest() *SignInPageTest {
+	var sip_test SignInPageTest
+
+	sip_test.opts = NewOptions()
+	sip_test.opts.Upstreams = append(sip_test.opts.Upstreams, "unused")
+	sip_test.opts.CookieSecret = "foobar"
+	sip_test.opts.ClientID = "bazquux"
+	sip_test.opts.ClientSecret = "xyzzyplugh"
+	sip_test.opts.Validate()
+
+	sip_test.proxy = NewOauthProxy(sip_test.opts, func(email string) bool {
+		return true
+	})
+	sip_test.sign_in_regexp = regexp.MustCompile(signInRedirectPattern)
+
+	return &sip_test
+}
+
+func (sip_test *SignInPageTest) GetEndpoint(endpoint string) (int, string) {
+	rw := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", endpoint, strings.NewReader(""))
+	sip_test.proxy.ServeHTTP(rw, req)
+	return rw.Code, rw.Body.String()
+}
+
+func TestSignInPageIncludesTargetRedirect(t *testing.T) {
+	sip_test := NewSignInPageTest()
+	const endpoint = "/some/random/endpoint"
+
+	code, body := sip_test.GetEndpoint(endpoint)
+	assert.Equal(t, 403, code)
+
+	match := sip_test.sign_in_regexp.FindStringSubmatch(body)
+	if match == nil {
+		t.Fatal("Did not find pattern in body: " +
+			signInRedirectPattern + "\nBody:\n" + body)
+	}
+	if match[1] != endpoint {
+		t.Fatal(`expected redirect to "` + endpoint +
+			`", but was "` + match[1] + `"`)
+	}
+}
+
+func TestSignInPageDirectAccessRedirectsToRoot(t *testing.T) {
+	sip_test := NewSignInPageTest()
+	code, body := sip_test.GetEndpoint("/oauth2/sign_in")
+	assert.Equal(t, 200, code)
+
+	match := sip_test.sign_in_regexp.FindStringSubmatch(body)
+	if match == nil {
+		t.Fatal("Did not find pattern in body: " +
+			signInRedirectPattern + "\nBody:\n" + body)
+	}
+	if match[1] != "/" {
+		t.Fatal(`expected redirect to "/", but was "` + match[1] + `"`)
+	}
+}