upload file to S3 gives cURL error 60: SSL certificate problem

I am trying to upload a file from s3. In config/filesystems.php I have defined all settings pertaining to s3. Then I am trying to upload a simple text file like this:

Storage::disk('s3')->put('file.txt', 'This is a test'); 

This gives the following error:

Error executing "PutObject" on "https://s3.amazonaws.com/my-bucket\file.txt"; AWS HTTP error: cURL error 60: SSL certificate problem: unable to get local issuer certificate (see http://curl.haxx.se/libcurl/c/libcurl-errors.html).

I have tried every thing under the sun. Including defining the curl.cainfo setting in php.ini as discussed here: https://laracasts.com/discuss/channels/general-discussion/curl-error-60-ssl-certificate-problem-unable-to-get-local-issuer-certificate

I am on windows. Any one got a clue to how to approach this?