oauth2/google: fix the logic of sts 0 value of expires_in

The sts response contains an optional field of `expires_in` and the value can be any integer.

https://github.com/golang/oauth2/blob/master/google/internal/externalaccount/basecredentials.go#L246-L248

In the case of less than `0`, we are going to throw an error. But in the case of equals to `0` practically it means "never expire" instead of "instantly expire" which doesn't make sense.

So we need to not set the expiration value for Token object. The current else if greater or equal is wrong.

It's never triggered only because we are sending positive `3600` in sts response.

Change-Id: Id227ca71130855235572b65ab178681e80d0da3a
GitHub-Last-Rev: a95c923
GitHub-Pull-Request: #687
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/545895
Reviewed-by: Shin Fan <shinfan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Cody Oss <codyoss@google.com>
Reviewed-by: Cody Oss <codyoss@google.com>

Author: BigTailWolf

google/externalaccount/basecredentials.go

@@ -471,11 +471,12 @@ func (ts tokenSource) Token() (*oauth2.Token, error) {
 		AccessToken: stsResp.AccessToken,
 		TokenType:   stsResp.TokenType,
 	}
-	if stsResp.ExpiresIn < 0 {
+
+	// The RFC8693 doesn't define the explicit 0 of "expires_in" field behavior.
+	if stsResp.ExpiresIn <= 0 {
 		return nil, fmt.Errorf("oauth2/google/externalaccount: got invalid expiry from security token service")
-	} else if stsResp.ExpiresIn >= 0 {
-		accessToken.Expiry = now().Add(time.Duration(stsResp.ExpiresIn) * time.Second)
 	}
+	accessToken.Expiry = now().Add(time.Duration(stsResp.ExpiresIn) * time.Second)
 
 	if stsResp.RefreshToken != "" {
 		accessToken.RefreshToken = stsResp.RefreshToken

google/externalaccount/basecredentials_test.go

@@ -6,6 +6,7 @@ package externalaccount
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"net/http"
@@ -101,15 +102,18 @@ func run(t *testing.T, config *Config, tets *testExchangeTokenServer) (*oauth2.T
 	return ts.Token()
 }
 
-func validateToken(t *testing.T, tok *oauth2.Token) {
-	if got, want := tok.AccessToken, correctAT; got != want {
+func validateToken(t *testing.T, tok *oauth2.Token, expectToken *oauth2.Token) {
+	if expectToken == nil {
+		return
+	}
+	if got, want := tok.AccessToken, expectToken.AccessToken; got != want {
 		t.Errorf("Unexpected access token: got %v, but wanted %v", got, want)
 	}
-	if got, want := tok.TokenType, "Bearer"; got != want {
+	if got, want := tok.TokenType, expectToken.TokenType; got != want {
 		t.Errorf("Unexpected TokenType: got %v, but wanted %v", got, want)
 	}
 
-	if got, want := tok.Expiry, testNow().Add(time.Duration(3600)*time.Second); got != want {
+	if got, want := tok.Expiry, expectToken.Expiry; got != want {
 		t.Errorf("Unexpected Expiry: got %v, but wanted %v", got, want)
 	}
 }
@@ -173,30 +177,91 @@ func getExpectedMetricsHeader(source string, saImpersonation bool, configLifetim
 }
 
 func TestToken(t *testing.T) {
-	config := Config{
-		Audience:         "32555940559.apps.googleusercontent.com",
-		SubjectTokenType: "urn:ietf:params:oauth:token-type:id_token",
-		ClientSecret:     "notsosecret",
-		ClientID:         "rbrgnognrhongo3bi4gb9ghg9g",
-		CredentialSource: &testBaseCredSource,
-		Scopes:           []string{"https://www.googleapis.com/auth/devstorage.full_control"},
+	type MockSTSResponse struct {
+		AccessToken     string `json:"access_token"`
+		IssuedTokenType string `json:"issued_token_type"`
+		TokenType       string `json:"token_type"`
+		ExpiresIn       int32  `json:"expires_in,omitempty"`
+		Scope           string `json:"scopre,omitenpty"`
 	}
 
-	server := testExchangeTokenServer{
-		url:           "/",
-		authorization: "Basic cmJyZ25vZ25yaG9uZ28zYmk0Z2I5Z2hnOWc6bm90c29zZWNyZXQ=",
-		contentType:   "application/x-www-form-urlencoded",
-		metricsHeader: getExpectedMetricsHeader("file", false, false),
-		body:          baseCredsRequestBody,
-		response:      baseCredsResponseBody,
+	testCases := []struct {
+		name           string
+		responseBody   MockSTSResponse
+		expectToken    *oauth2.Token
+		expectErrorMsg string
+	}{
+		{
+			name: "happy case",
+			responseBody: MockSTSResponse{
+				AccessToken:     correctAT,
+				IssuedTokenType: "urn:ietf:params:oauth:token-type:access_token",
+				TokenType:       "Bearer",
+				ExpiresIn:       3600,
+				Scope:           "https://www.googleapis.com/auth/cloud-platform",
+			},
+			expectToken: &oauth2.Token{
+				AccessToken: correctAT,
+				TokenType:   "Bearer",
+				Expiry:      testNow().Add(time.Duration(3600) * time.Second),
+			},
+		},
+		{
+			name: "no expiry time on token",
+			responseBody: MockSTSResponse{
+				AccessToken:     correctAT,
+				IssuedTokenType: "urn:ietf:params:oauth:token-type:access_token",
+				TokenType:       "Bearer",
+				Scope:           "https://www.googleapis.com/auth/cloud-platform",
+			},
+			expectToken:    nil,
+			expectErrorMsg: "oauth2/google/externalaccount: got invalid expiry from security token service",
+		},
+		{
+			name: "negative expiry time",
+			responseBody: MockSTSResponse{
+				AccessToken:     correctAT,
+				IssuedTokenType: "urn:ietf:params:oauth:token-type:access_token",
+				TokenType:       "Bearer",
+				ExpiresIn:       -1,
+				Scope:           "https://www.googleapis.com/auth/cloud-platform",
+			},
+			expectToken:    nil,
+			expectErrorMsg: "oauth2/google/externalaccount: got invalid expiry from security token service",
+		},
 	}
 
-	tok, err := run(t, &config, &server)
+	for _, testCase := range testCases {
+		config := Config{
+			Audience:         "32555940559.apps.googleusercontent.com",
+			SubjectTokenType: "urn:ietf:params:oauth:token-type:id_token",
+			ClientSecret:     "notsosecret",
+			ClientID:         "rbrgnognrhongo3bi4gb9ghg9g",
+			CredentialSource: &testBaseCredSource,
+			Scopes:           []string{"https://www.googleapis.com/auth/devstorage.full_control"},
+		}
 
-	if err != nil {
-		t.Fatalf("Unexpected error: %e", err)
+		responseBody, err := json.Marshal(testCase.responseBody)
+		if err != nil {
+			t.Errorf("Invalid response received.")
+		}
+
+		server := testExchangeTokenServer{
+			url:           "/",
+			authorization: "Basic cmJyZ25vZ25yaG9uZ28zYmk0Z2I5Z2hnOWc6bm90c29zZWNyZXQ=",
+			contentType:   "application/x-www-form-urlencoded",
+			metricsHeader: getExpectedMetricsHeader("file", false, false),
+			body:          baseCredsRequestBody,
+			response:      string(responseBody),
+		}
+
+		tok, err := run(t, &config, &server)
+
+		if err != nil && err.Error() != testCase.expectErrorMsg {
+			t.Errorf("Error not as expected: got = %v, and want = %v", err, testCase.expectErrorMsg)
+		}
+		validateToken(t, tok, testCase.expectToken)
 	}
-	validateToken(t, tok)
 }
 
 func TestWorkforcePoolTokenWithClientID(t *testing.T) {
@@ -224,7 +289,12 @@ func TestWorkforcePoolTokenWithClientID(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Unexpected error: %e", err)
 	}
-	validateToken(t, tok)
+	expectToken := oauth2.Token{
+		AccessToken: correctAT,
+		TokenType:   "Bearer",
+		Expiry:      testNow().Add(time.Duration(3600) * time.Second),
+	}
+	validateToken(t, tok, &expectToken)
 }
 
 func TestWorkforcePoolTokenWithoutClientID(t *testing.T) {
@@ -251,7 +321,12 @@ func TestWorkforcePoolTokenWithoutClientID(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Unexpected error: %e", err)
 	}
-	validateToken(t, tok)
+	expectToken := oauth2.Token{
+		AccessToken: correctAT,
+		TokenType:   "Bearer",
+		Expiry:      testNow().Add(time.Duration(3600) * time.Second),
+	}
+	validateToken(t, tok, &expectToken)
 }
 
 func TestNonworkforceWithWorkforcePoolUserProject(t *testing.T) {