Hopefully you have a solution by now, if not see https://community.jboss.org/message/761570#761570
I had a similar problem with encrypted credentials passed in a cookie, adding the following system properties to standalone.xml resolved it:
<property name="org.apache.catalina.STRICT_SERVLET_COMPLIANCE" value="false"/>
<property name="org.apache.tomcat.util.http.ServerCookie.ALLOW_EQUALS_IN_VALUE" value="true"/>
<property name="org.apache.tomcat.util.http.ServerCookie.ALLOW_HTTP_SEPARATORS_IN_V0" value="true"/>
<property name="org.apache.tomcat.util.http.ServerCookie.ALWAYS_ADD_EXPIRES" value="false"/>
<property name="org.apache.tomcat.util.http.ServerCookie.FWD_SLASH_IS_SEPARATOR" value="false"/>