proxy: add per-route request headers setting (#346)

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

proxy/middleware_test.go

@@ -6,9 +6,11 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
+	"github.com/google/go-cmp/cmp"
 	"github.com/pomerium/pomerium/internal/identity"
 	"github.com/pomerium/pomerium/internal/sessions"
 	"github.com/pomerium/pomerium/proxy/clients"
@@ -173,3 +175,40 @@ func TestProxy_SignRequest(t *testing.T) {
 		})
 	}
 }
+
+func TestProxy_SetResponseHeaders(t *testing.T) {
+	t.Parallel()
+	fn := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.Header().Set("X-Content-Type-Options", "nosniff")
+		var sb strings.Builder
+		for k, v := range r.Header {
+			k = strings.ToLower(k)
+			for _, h := range v {
+				sb.WriteString(fmt.Sprintf("%v: %v\n", k, h))
+			}
+		}
+		fmt.Fprint(w, sb.String())
+		w.WriteHeader(http.StatusOK)
+	})
+	tests := []struct {
+		name        string
+		setHeaders  map[string]string
+		wantHeaders string
+	}{
+		{"good", map[string]string{"x-gonna": "give-it-to-ya"}, "x-gonna: give-it-to-ya\n"},
+		{"nil", nil, ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+
+			r := httptest.NewRequest(http.MethodGet, "/", nil)
+			w := httptest.NewRecorder()
+			got := SetResponseHeaders(tt.setHeaders)(fn)
+			got.ServeHTTP(w, r)
+			if diff := cmp.Diff(w.Body.String(), tt.wantHeaders); diff != "" {
+				t.Errorf("SignRequest() :\n %s", diff)
+			}
+		})
+	}
+}