HttpServletRequest within Credentials contains no parameters

Although the HTTP request is made available to authentication providers, calls to getParameter() and getParameterMap() will fail, returning null or an empty map respectively, because Jersey / JAX-RS consumes the request earlier on, likely via getInputStream() or getReader().

See: https://sourceforge.net/p/guacamole/discussion/1110834/thread/e22f94a8/

Tegereo was able to pass the extra un-recognized parameters by adding a MultivaluedMap to createToken (see attached patch). A more transparent workaround, documented on StackOverflow, would be to wrap the request using HttpServletRequestWrapper, reimplementing getParameter() and getParameterMap() to use this MultivaluedMap: http://stackoverflow.com/questions/22376810/unable-to-retrive-post-data-using-context-httpservletrequest-when-passed-to-oa

Wrapping the request should allow previously-implemented plugins to "just work" again.