How to pass custom parameters from client to UniMRCP plugin

Question

Actually I wanted to get custom params in plugin from client I tried pass params from extension.conf like below:

exten => s,2, SynthAndRecog(Welcome to bot,builtin:speech/transcribe, userdid=user_id&spl=en-IN&p=speech-nuance5-mrcp2)

But I'm not getting it in plugin. Here is the plugin code to get param:

while((header_field = mrcp_message_next_header_field_get(request,header_field)) != NULL ) {
       printf("\n===============params================\n");
       printf("%s: %s\n", header_field->name.buf, header_field->value.buf);

}