Return error messages for authentication errors (#950)

Previously the authorization middleware was masking the error when
authentication failed.

server/service/middleware/authzcheck/authzcheck.go

@@ -6,11 +6,13 @@ package authzcheck
 
 import (
 	"context"
+	"errors"
 	"reflect"
 	"runtime"
 
 	"github.com/fleetdm/fleet/server/authz"
 	authz_ctx "github.com/fleetdm/fleet/server/contexts/authz"
+	"github.com/fleetdm/fleet/server/kolide"
 	"github.com/go-kit/kit/endpoint"
 )
 
@@ -28,7 +30,15 @@ func (m *Middleware) AuthzCheck() endpoint.Middleware {
 			authzctx := &authz_ctx.AuthorizationContext{}
 			ctx = authz_ctx.NewContext(ctx, authzctx)
 
-			response, error := next(ctx, req)
+			response, err := next(ctx, req)
+
+			// If authentication check failed, return that error (so that we log
+			// appropriately).
+			var authFailedError *kolide.AuthFailedError
+			var authRequiredError *kolide.AuthRequiredError
+			if errors.As(err, &authFailedError) || errors.As(err, &authRequiredError) {
+				return nil, err
+			}
 
 			// If authorization was not checked, return a response that will
 			// marshal to a generic error and log that the check was missed.
@@ -37,7 +47,7 @@ func (m *Middleware) AuthzCheck() endpoint.Middleware {
 				return nil, authz.ForbiddenWithInternal("missed authz check: " + funcName)
 			}
 
-			return response, error
+			return response, err
 		}
 	}
 }

server/service/middleware/authzcheck/authzcheck_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/fleetdm/fleet/server/contexts/authz"
+	"github.com/fleetdm/fleet/server/kolide"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -26,6 +27,36 @@ func TestAuthzCheck(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+func TestAuthzCheckAuthFailed(t *testing.T) {
+	t.Parallel()
+
+	checker := NewMiddleware()
+
+	check := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return nil, kolide.NewAuthFailedError("failed")
+	}
+	check = checker.AuthzCheck()(check)
+
+	_, err := check(context.Background(), struct{}{})
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "failed")
+}
+
+func TestAuthzCheckAuthRequired(t *testing.T) {
+	t.Parallel()
+
+	checker := NewMiddleware()
+
+	check := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return nil, kolide.NewAuthRequiredError("required")
+	}
+	check = checker.AuthzCheck()(check)
+
+	_, err := check(context.Background(), struct{}{})
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "required")
+}
+
 func TestAuthzCheckMissing(t *testing.T) {
 	t.Parallel()