Add cookie subject extractor

pkg/config/env.go

@@ -204,6 +204,12 @@ var Config = struct {
 	HeaderAuthEnabled   bool   `env:"FLAGR_HEADER_AUTH_ENABLED" envDefault:"false"`
 	HeaderAuthUserField string `env:"FLAGR_HEADER_AUTH_USER_FIELD" envDefault:"X-Email"`
 
+	// Identify users through cookies
+	// E.g. via cloudflare zero trust, we derive the user email from the JWT token stored in the cookie of CF_Authorization
+	CookieAuthEnabled           bool   `env:"FLAGR_COOKIE_AUTH_ENABLED" envDefault:"false"`
+	CookieAuthUserField         string `env:"FLAGR_COOKIE_AUTH_USER_FIELD" envDefault:"CF_Authorization"`
+	CookieAuthUserFieldJWTClaim string `env:"FLAGR_COOKIE_AUTH_USER_FIELD_JWT_CLAIM" envDefault:"email"`
+
 	// Authenticate with basic auth
 	BasicAuthEnabled              bool     `env:"FLAGR_BASIC_AUTH_ENABLED" envDefault:"false"`
 	BasicAuthUsername             string   `env:"FLAGR_BASIC_AUTH_USERNAME" envDefault:""`

pkg/handler/subject.go

@@ -26,6 +26,21 @@ func getSubjectFromRequest(r *http.Request) string {
 
 	} else if config.Config.HeaderAuthEnabled {
 		return r.Header.Get(config.Config.HeaderAuthUserField)
+	} else if config.Config.CookieAuthEnabled {
+		c, err := r.Cookie(config.Config.CookieAuthUserField)
+		if err != nil {
+			return ""
+		}
+		if config.Config.CookieAuthUserFieldJWTClaim != "" {
+			// for this case, we choose to skip the error check because just like HeaderAuthUserField
+			// in the future, we can extend this function to support cookie jwt token validation
+			// this assumes that the cookie we get already passed the auth middleware
+			token, _ := jwt.Parse(c.Value, func(token *jwt.Token) (interface{}, error) { return "", nil })
+			if claims, ok := token.Claims.(jwt.MapClaims); ok {
+				return util.SafeString(claims[config.Config.CookieAuthUserFieldJWTClaim])
+			}
+		}
+		return c.Value
 	}
 
 	return ""

pkg/handler/subject_test.go

@@ -48,3 +48,31 @@ func TestGetSubjectFromOauthProxy(t *testing.T) {
 	r.Header.Set(config.Config.HeaderAuthUserField, "[email protected]")
 	assert.Equal(t, getSubjectFromRequest(r.WithContext(ctx)), "[email protected]")
 }
+
+func TestGetSubjectFromCookie(t *testing.T) {
+	var ctx = context.Background()
+	defer func() { config.Config.CookieAuthEnabled = false }()
+	config.Config.CookieAuthEnabled = true
+
+	t.Run("test HS256 happy codepath", func(t *testing.T) {
+		r, _ := http.NewRequest("GET", "", nil)
+		assert.Equal(t, getSubjectFromRequest(r), "")
+
+		r.AddCookie(&http.Cookie{
+			Name:  config.Config.CookieAuthUserField,
+			Value: "eyJhbGciOiJIUzI1NiIsImtpZCI6IjEyMzQ1In0.eyJzdWIiOiIxMjM0NTY3ODkwIiwiZW1haWwiOiJhYmNAZXhhbXBsZS5jb20iLCJpYXQiOjE1MTYyMzkwMjJ9.tzRXenFic8Eqg2awzO0eiX6Rozy_mmsJVzLJfUUfREI",
+		})
+		assert.Equal(t, getSubjectFromRequest(r.WithContext(ctx)), "[email protected]")
+	})
+
+	t.Run("test HS256 empty claim", func(t *testing.T) {
+		r, _ := http.NewRequest("GET", "", nil)
+		assert.Equal(t, getSubjectFromRequest(r), "")
+
+		r.AddCookie(&http.Cookie{
+			Name:  config.Config.CookieAuthUserField,
+			Value: "eyJhbGciOiJIUzI1NiIsImtpZCI6IjEyMzQ1In0.eyJzdWIiOiIxMjM0NTY3ODkwIiwiaWF0IjoxNTE2MjM5MDIyfQ.C_YsEkcHa7aSVQILzJAayFgJk-sj1cmNWIWUm7m7vy4",
+		})
+		assert.Equal(t, getSubjectFromRequest(r.WithContext(ctx)), "")
+	})
+}