Hi,
I think you are missing the http accept header which also needs to be sent. Saying which API version you are trying to access.
Once authenticated the API sends back a token which also needs to be sent for the subsequent API calls post login.
Accept Header
For API 5.1
Key: Accept
Value: application/*+xml;version=5.1
For API 1.5
Key: Accept
Value: application/*+xml;version=1.5
Once authenticated, you need to send the token for the subsequent API calls that you make
Key: x-vcloud-authorization
Value: 0SRZvfyGSOklo5J+DqP9bCshB/23TBdwoSR4FWqkw20=
Regards,
Rajesh Kamal.