How to send a POST request to AWS for Amazon Lex service

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I have tried sending a POST request to my Lex bot using the in-built AWS signature call in the Postman app with my text inside a JSON with key as inputText and it works perfectly well. Now I want to do the same using my JS script in which I make an Ajax call. But I do not know the headers that are to be sent in the request; namely the Access Key, Secret Key, Region Name, Service Name. Any help on how can I make an Ajax call to my Lex bot using JS ?