I need some help with getting Auth Token through Postman. Based on https://help.salesforce.com/HTViewHelpDoc?id=remoteaccess_oauth_username_password_flow.htm&language=en_US I have constructed a request . cs10 - is the right sales force instance, query params are also correct, but something is wrong. Not sure what is missing. Thanks.
This is an old question, but I have recently faced a similar issue and I thought I would rather post a more detailed answer than the one I posted initially.
I managed to get authentication via Postman. The key for me was to create a [Connected app] (https://help.salesforce.com/apex/HTViewHelpDoc?id=connected_app_overview.htm) and to connect using the "authorization code" grant type in OAuth.
I also wrote a step-by-step guide here: