add cors_allow_preflight option to route policy

internal/middleware/middleware.go

@@ -117,10 +117,10 @@ func ValidateSignature(sharedSecret string) func(next http.Handler) http.Handler
 }
 
 // ValidateHost ensures that each request's host is valid
-func ValidateHost(mux map[string]http.Handler) func(next http.Handler) http.Handler {
+func ValidateHost(validHost func(host string) bool) func(next http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if _, ok := mux[r.Host]; !ok {
+			if !validHost(r.Host) {
 				httputil.ErrorResponse(w, r, "Unknown route", http.StatusNotFound)
 				return
 			}

internal/middleware/middleware_test.go

@@ -292,18 +292,22 @@ func handlerHelp(msg string) http.Handler {
 	return &handlerHelper{msg}
 }
 func TestValidateHost(t *testing.T) {
-	m := make(map[string]http.Handler)
-	m["google.com"] = handlerHelp("google")
+	validHostFunc := func(host string) bool {
+		return host == "google.com"
+	}
+
+	validHostHandler := handlerHelp("google")
 
 	tests := []struct {
 		name             string
-		validHosts map[string]http.Handler
+		isValidHost      func(string) bool
+		validHostHandler http.Handler
 		clientPath       string
 		expected         []byte
 		status           int
 	}{
-		{"good", m, "google.com", []byte("google"), 200},
-		{"no route", m, "googles.com", []byte("google"), 404},
+		{"good", validHostFunc, validHostHandler, "google.com", []byte("google"), 200},
+		{"no route", validHostFunc, validHostHandler, "googles.com", []byte("google"), 404},
 	}
 
 	for _, tt := range tests {
@@ -315,13 +319,13 @@ func TestValidateHost(t *testing.T) {
 			rr := httptest.NewRecorder()
 
 			var testHandler http.Handler
-			if tt.validHosts[tt.clientPath] != nil {
-				tt.validHosts[tt.clientPath].ServeHTTP(rr, req)
-				testHandler = tt.validHosts[tt.clientPath]
+			if tt.isValidHost(tt.clientPath) {
+				tt.validHostHandler.ServeHTTP(rr, req)
+				testHandler = tt.validHostHandler
 			} else {
 				testHandler = handlerHelp("ok")
 			}
-			handler := ValidateHost(tt.validHosts)(testHandler)
+			handler := ValidateHost(tt.isValidHost)(testHandler)
 			handler.ServeHTTP(rr, req)
 
 			if rr.Code != tt.status {

internal/policy/policy.go

@@ -26,6 +26,10 @@ type Policy struct {
 
 	Source      *url.URL
 	Destination *url.URL
+
+	// Allow unauthenticated HTTP OPTIONS requests as per the CORS spec
+	// https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#Preflighted_requests
+	CORSAllowPreflight bool `yaml:"cors_allow_preflight"`
 }
 
 func (p *Policy) validate() (err error) {

policy.example.yaml

@@ -17,3 +17,8 @@
   to: http://hello:8080
   allowed_groups:
     - admins
+- from: cross-origin.corp.beyondperimeter.com 
+  to: httpbin.org
+  allowed_domains:
+      - gmail.com
+  cors_allow_preflight: true

proxy/handlers.go

@@ -14,6 +14,7 @@ import (
 	"github.com/pomerium/pomerium/internal/httputil"
 	"github.com/pomerium/pomerium/internal/log"
 	"github.com/pomerium/pomerium/internal/middleware"
+	"github.com/pomerium/pomerium/internal/policy"
 	"github.com/pomerium/pomerium/internal/sessions"
 	"github.com/pomerium/pomerium/internal/version"
 )
@@ -68,7 +69,10 @@ func (p *Proxy) Handler() http.Handler {
 	c = c.Append(middleware.UserAgentHandler("user_agent"))
 	c = c.Append(middleware.RefererHandler("referer"))
 	c = c.Append(middleware.RequestIDHandler("req_id", "Request-Id"))
-	c = c.Append(middleware.ValidateHost(p.mux))
+	c = c.Append(middleware.ValidateHost(func(host string) bool {
+		_, ok := p.routeConfigs[host]
+		return ok
+	}))
 
 	// serve the middleware and mux
 	return c.Then(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -223,9 +227,33 @@ func (p *Proxy) OAuthCallback(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, stateParameter.RedirectURI, http.StatusFound)
 }
 
+// shouldSkipAuthentication contains conditions for skipping authentication.
+// Conditions should be few in number and have strong justifications.
+func (p *Proxy) shouldSkipAuthentication(r *http.Request) bool {
+	pol, foundPolicy := p.policy(r)
+
+	if isCORSPreflight(r) && foundPolicy && pol.CORSAllowPreflight {
+		log.FromRequest(r).Debug().Msg("proxy: skipping authentication for valid CORS preflight request")
+		return true
+	}
+
+	return false
+}
+
+// isCORSPreflight inspects the request to see if this is a valid CORS preflight request.
+// These checks are not exhaustive, because the proxied server should be verifying it as well.
+//
+// See https://www.html5rocks.com/static/images/cors_server_flowchart.png for more info.
+func isCORSPreflight(r *http.Request) bool {
+	return r.Method == http.MethodOptions &&
+		r.Header.Get("Access-Control-Request-Method") != "" &&
+		r.Header.Get("Origin") != ""
+}
+
 // Proxy authenticates a request, either proxying the request if it is authenticated,
 // or starting the authenticate service for validation if not.
 func (p *Proxy) Proxy(w http.ResponseWriter, r *http.Request) {
+	if !p.shouldSkipAuthentication(r) {
 		err := p.Authenticate(w, r)
 		// If the authenticate is not successful we proceed to start the OAuth Flow with
 		// OAuthStart. If successful, we proceed to proxy to the configured upstream.
@@ -253,6 +281,8 @@ func (p *Proxy) Proxy(w http.ResponseWriter, r *http.Request) {
 			httputil.ErrorResponse(w, r, "Access unauthorized", http.StatusForbidden)
 			return
 		}
+	}
+
 	// We have validated the users request and now proxy their request to the provided upstream.
 	route, ok := p.router(r)
 	if !ok {
@@ -325,17 +355,31 @@ func (p *Proxy) Authenticate(w http.ResponseWriter, r *http.Request) (err error)
 }
 
 // Handle constructs a route from the given host string and matches it to the provided http.Handler and UpstreamConfig
-func (p *Proxy) Handle(host string, handler http.Handler) {
-	p.mux[host] = handler
+func (p *Proxy) Handle(host string, handler http.Handler, pol *policy.Policy) {
+	p.routeConfigs[host] = &routeConfig{
+		mux:    handler,
+		policy: pol,
+	}
 }
 
 // router attempts to find a route for a request. If a route is successfully matched,
 // it returns the route information and a bool value of `true`. If a route can not be matched,
 // a nil value for the route and false bool value is returned.
 func (p *Proxy) router(r *http.Request) (http.Handler, bool) {
-	route, ok := p.mux[r.Host]
+	config, ok := p.routeConfigs[r.Host]
 	if ok {
-		return route, true
+		return config.mux, true
+	}
+	return nil, false
+}
+
+// policy attempts to find a policy for a request. If a policy is successfully matched,
+// it returns the policy information and a bool value of `true`. If a policy can not be matched,
+// a nil value for the policy and false bool value is returned.
+func (p *Proxy) policy(r *http.Request) (*policy.Policy, bool) {
+	config, ok := p.routeConfigs[r.Host]
+	if ok {
+		return config.policy, true
 	}
 	return nil, false
 }

proxy/handlers_test.go

@@ -352,8 +352,22 @@ func TestProxy_Proxy(t *testing.T) {
 		RefreshDeadline:  time.Now().Add(10 * time.Second),
 	}
 
+	opts := testOptions()
+	optsCORS := testOptionsWithCORS()
+
+	defaultHeaders, goodCORSHeaders, badCORSHeaders := http.Header{}, http.Header{}, http.Header{}
+
+	goodCORSHeaders.Set("origin", "anything")
+	goodCORSHeaders.Set("access-control-request-method", "anything")
+
+	// missing "Origin"
+	badCORSHeaders.Set("access-control-request-method", "anything")
+
 	tests := []struct {
 		name          string
+		options       *Options
+		method        string
+		header        http.Header
 		host          string
 		session       sessions.SessionStore
 		authenticator clients.Authenticator
@@ -361,16 +375,20 @@ func TestProxy_Proxy(t *testing.T) {
 		wantStatus    int
 	}{
 		// weirdly, we want 503 here because that means proxy is trying to route a domain (example.com) that we dont control. Weird. I know.
-		{"good", "https://corp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: true}, http.StatusServiceUnavailable},
-		{"unexpected error", "https://corp.example.com/test", &sessions.MockSessionStore{LoadError: errors.New("ok")}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: true}, http.StatusInternalServerError},
+		{"good", opts, http.MethodGet, defaultHeaders, "https://corp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: true}, http.StatusServiceUnavailable},
+		{"good cors preflight", optsCORS, http.MethodOptions, goodCORSHeaders, "https://corp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: false}, http.StatusServiceUnavailable},
+		// same request as above, but with cors_allow_preflight=false in the policy
+		{"valid cors, but not allowed", opts, http.MethodOptions, goodCORSHeaders, "https://corp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: false}, http.StatusForbidden},
+		// cors allowed, but the request is missing proper headers
+		{"invalid cors headers", optsCORS, http.MethodOptions, badCORSHeaders, "https://corp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: false}, http.StatusForbidden},
+		{"unexpected error", opts, http.MethodGet, defaultHeaders, "https://corp.example.com/test", &sessions.MockSessionStore{LoadError: errors.New("ok")}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: true}, http.StatusInternalServerError},
 		// redirect to start auth process
-		{"unknown host", "https://notcorp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: true}, http.StatusNotFound},
-		{"user forbidden", "https://notcorp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: false}, http.StatusForbidden},
+		{"unknown host", opts, http.MethodGet, defaultHeaders, "https://notcorp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: true}, http.StatusNotFound},
+		{"user forbidden", opts, http.MethodGet, defaultHeaders, "https://notcorp.example.com/test", &sessions.MockSessionStore{Session: goodSession}, clients.MockAuthenticate{}, clients.MockAuthorize{AuthorizeResponse: false}, http.StatusForbidden},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			opts := testOptions()
-			p, err := New(opts)
+			p, err := New(tt.options)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -379,7 +397,8 @@ func TestProxy_Proxy(t *testing.T) {
 			p.AuthenticateClient = tt.authenticator
 			p.AuthorizeClient = tt.authorizer
 
-			r := httptest.NewRequest("GET", tt.host, nil)
+			r := httptest.NewRequest(tt.method, tt.host, nil)
+			r.Header = tt.header
 			w := httptest.NewRecorder()
 			p.Proxy(w, r)
 			if status := w.Code; status != tt.wantStatus {

proxy/proxy.go

@@ -174,7 +174,12 @@ type Proxy struct {
 
 	redirectURL  *url.URL
 	templates    *template.Template
-	mux         map[string]http.Handler
+	routeConfigs map[string]*routeConfig
+}
+
+type routeConfig struct {
+	mux    http.Handler
+	policy *policy.Policy
 }
 
 // New takes a Proxy service from options and a validation function.
@@ -208,7 +213,7 @@ func New(opts *Options) (*Proxy, error) {
 	}
 
 	p := &Proxy{
-		mux: make(map[string]http.Handler),
+		routeConfigs: make(map[string]*routeConfig),
 		// services
 		AuthenticateURL: opts.AuthenticateURL,
 		// session state
@@ -232,7 +237,7 @@ func New(opts *Options) (*Proxy, error) {
 		if err != nil {
 			return nil, err
 		}
-		p.Handle(route.Source.Host, handler)
+		p.Handle(route.Source.Host, handler, &route)
 		log.Info().Str("src", route.Source.Host).Str("dst", route.Destination.Host).Msg("proxy: new route")
 	}
 

proxy/proxy_test.go

@@ -127,6 +127,13 @@ func testOptions() *Options {
 	}
 }
 
+func testOptionsWithCORS() *Options {
+	configBlob := `[{"from":"corp.example.com","to":"example.com","cors_allow_preflight":true}]` //valid yaml
+	opts := testOptions()
+	opts.Policy = base64.URLEncoding.EncodeToString([]byte(configBlob))
+	return opts
+}
+
 func TestOptions_Validate(t *testing.T) {
 	good := testOptions()
 	badFromRoute := testOptions()
@@ -204,7 +211,7 @@ func TestNew(t *testing.T) {
 		opts      *Options
 		optFuncs  []func(*Proxy) error
 		wantProxy bool
-		numMuxes  int
+		numRoutes int
 		wantErr   bool
 	}{
 		{"good", good, nil, true, 1, false},
@@ -223,8 +230,8 @@ func TestNew(t *testing.T) {
 			if got == nil && tt.wantProxy == true {
 				t.Errorf("New() expected valid proxy struct")
 			}
-			if got != nil && len(got.mux) != tt.numMuxes {
-				t.Errorf("New() = num muxes \n%+v, want \n%+v", got, tt.numMuxes)
+			if got != nil && len(got.routeConfigs) != tt.numRoutes {
+				t.Errorf("New() = num routeConfigs \n%+v, want \n%+v", got, tt.numRoutes)
 			}
 		})
 	}