authorization_code flow

[gtata]

I tried the following for authorization code flow but it running into an error.

Using Postman with the following inputs:

Method=POST
URL=
http://localhost:8080/oauth/authorize?response_type=code&client_id=sso-auth-client&redirect_uri=http://localhost:8383/oauth/callback/handler

Authorization=Basic Auth
username: user@awesome.com
password: cant_hack_this

And the response I get is as follows:

{
"error": "unauthorized",
"error_description": "An Authentication object was not found in the SecurityContext"
}

What am I missing in my request?

Thanks.

Gabsaga