How to store secure variable values in .http files in Visual Studio? – Stack Overflow

Add a file called http-client.env.json in the same directory as the .http file. By default, this file is set to check into source control.
This file can be left blank, if you don’t have any values checked in.

{ }

Add another file called http-client.env.json.user in the same directory. This is where the secret values go in. By default, this file is set not to check into source control.
In this file you can set the secrets under an environment root,

{
  "dev": {
    "Username": "myusername1",
    "Password": "mypassword1"
  },
  "prod": {
    "Username": "myusername2",
    "Password": "mypassword2"
  }
}

Now in the .http file access the defined variable using {{ }},
In this example, the environment variable file values are read into .http file variables,

@UsernameVar = {{Username}}
@PasswordVar = {{Password}}

then used as needed,

POST {{MyAuth.Auth_HostAddress}}/api/v1/auth/login
Content-Type: application/json
{
    "username": "{{UsernameVar}}",
    "password": "{{PasswordVar}}"
}

Finally you can switch environments from the defined list of environemnts in the top right corner of Visual Studio .http file editor,