A request from Canvas will have keys with multiple values such as
ext_outcome_data_values_accepted=[url,text]
If you aren't implementing a servlet (e.g. in a Play framework application), you cannot use LTIVerifier.verifyParameters. There is no Map<String, String> that you can pass.
You need to be able to pass a Map<String, String[]> or a similar multi-valued map.
Also, are you including key/value pairs in the url in the verification? If so, it would be good to clearly state that in the docs. If not, that would be a useful service to provide.