SNOW-1206259 Handle OKTA Auth invalid responses more gracefully (#884)

### Description
Native OKTA SSO Authn improvements of error handling. 

### Checklist
- [x] Code compiles correctly
- [x] Code is formatted according to [Coding
Conventions](../CodingConventions.md)
- [x] Created tests which fail without the change (if possible)
- [x] All tests passing (`dotnet test`)
- [x] Extended the README / documentation, if necessary
- [x] Provide JIRA issue id (if possible) or GitHub issue id in PR name

Snowflake.Data.Tests/IntegrationTests/SFConnectionIT.cs

@@ -2153,6 +2153,22 @@ public void TestAsyncOktaConnectionUntilMaxTimeout()
                 }
             }
         }
+
+        [Test]
+        [Ignore("This test requires established dev Okta SSO and credentials matching Snowflake user")]
+        public void TestNativeOktaSuccess()
+        {
+            var oktaUrl = "https://***.okta.com/";
+            var oktaUser = "***";
+            var oktaPassword = "***";
+            using (IDbConnection conn = new SnowflakeDbConnection())
+            {
+                conn.ConnectionString = ConnectionStringWithoutAuth + 
+                                        $";authenticator={oktaUrl};user={oktaUser};password={oktaPassword};";
+                conn.Open();
+                Assert.AreEqual(ConnectionState.Open, conn.State);
+            }
+        }
     }
 }