sfmc-api-v1-authentication-ssjs.html

<script runat="server">
Platform.Load("Core","1.1.1");

var authEndpoint = 'https://mcxxxxxxxxxxxxxxxxxxxxxxxxx.auth.marketingcloudapis.com';
var payload = {
        clientId: "insert Client Id",
        clientSecret: "insert Client Secret"
    };
var url = authEndpoint + '/v1/requestToken';  
var contentType = 'application/json';

try {
   var accessTokenRequest = HTTP.Post(url, contentType, Stringify(payload));
   if(accessTokenRequest.StatusCode == 200) {
        var tokenResponse = Platform.Function.ParseJSON(accessTokenRequest.Response[0]);
        var accessToken = tokenResponse.accessToken;
   }
} catch (error) {
    Write(Stringify(error));
}
</script>