I am using
https://api.twitter.com/oauth/request_token
for the URL. I am using header-based authentication. The Authorization header looks like this:
OAuth oauth_nonce=“53b833b3808114c166d5b95eccf986ba4bb95b5d”,oauth_callback=“oob”,oauth_signature_method=“HMAC-SHA1”,oauth_timestamp=“1315414189”,oauth_consumer_key=“fy5lC1V4ojgaolKPnEsbg”,oauth_version=“1.0”,oauth_signature=“2OMyNDRK49sHNy/uknDwWOfjm9A=”
Thanks.