Extract credentials from HTTP path query string even when non-terminal parameter

[jfallows]

HTTP path query string can consist of multiple parameters separated by &.

When configured to extract credentials from path query string such as...

                        "credentials":
                        {
                            "query":
                            {
                                "access_token": "{credentials}"
                            }
                        }

...then make sure requests such as the following still extract TOKEN as expected.

https://localhost:9090/?access_token=TOKEN&parameter=value