Variables in place of HardCode values

            string email = "myemail";
            string password = "mypassword";
            var body =  "{\n" +
                        $"    \"email\" : \"{email}\",\n" +
                        $"    \"password\" : \"{password}\"\n" +
                        "}";

However; you're better off using Environment.NewLine as that will conform to your operating system.

            string email = "myemail";
            string password = "mypassword";
            var body = "{" + Environment.NewLine +
            $"    \"email\" : \"{email}\"," + Environment.NewLine +
            $"    \"password\" : \"{password}\"" + Environment.NewLine +
            "}";

And if you are using C# 11 and .NET 7, this works:

 

            string email = "myemail";
            string password = "mypassword";
            var body = """
            {
                "email" : "{email}",
                "password" : "{password}"
            )
            """;