fix: missing expiration_time field isn't a problem for executables

Change-Id: Ib19e3d9dcd8a4c41afebf2a1fb97429617eef86b
GitHub-Last-Rev: 96eb2344dee49b7c08aca5c728c0f4d9ec4634b8
GitHub-Pull-Request: golang/oauth2#576
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/418434
Reviewed-by: Leo Siracusa <leosiracusa@google.com>
Run-TryBot: Cody Oss <codyoss@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cody Oss <codyoss@google.com>

google/internal/externalaccount/executablecredsource_test.go

@@ -388,19 +388,6 @@ var failureTests = []struct {
 		expectedErr: missingFieldError(executableSource, "token_type"),
 	},
 
-	{
-		name: "Missing Expiration",
-		testEnvironment: testEnvironment{
-			envVars: executablesAllowed,
-			jsonResponse: &executableResponse{
-				Success:   Bool(true),
-				Version:   1,
-				TokenType: "urn:ietf:params:oauth:token-type:jwt",
-			},
-		},
-		expectedErr: missingFieldError(executableSource, "expiration_time"),
-	},
-
 	{
 		name: "Token Expired",
 		testEnvironment: testEnvironment{
@@ -564,6 +551,19 @@ var successTests = []struct {
 			},
 		},
 	},
+
+	{
+		name: "Missing Expiration",
+		testEnvironment: testEnvironment{
+			envVars: executablesAllowed,
+			jsonResponse: &executableResponse{
+				Success:   Bool(true),
+				Version:   1,
+				TokenType: "urn:ietf:params:oauth:token-type:jwt",
+				IdToken:   "tokentokentoken",
+			},
+		},
+	},
 }
 
 func TestRetrieveExecutableSubjectTokenSuccesses(t *testing.T) {