TeamDynamix Authentication and Authorizartion

I've used the .net c# utility to import people into TeamDynamix, but now my process is going to move to a linux environment, so I need a different way of getting this to work.  How can that be done?  In the c# project, the import is accomplished through a function call and the use of some api library .dll files.  How can I move this to a linux environment ?

Thank you

Now I'm trying to get a JSON formatted respone in Postman using the following script, how can I do this?  I'm getting a HTML formatted response as if the authentication isn't working

the code below is placed in the pre request script portion of the postman sections.

const tokenUrl = 'https://support.csuchico.edu/SBTDWebApi/';

pm.sendRequest({
    url: tokenUrl,
    method: 'POST',
    body: {
        'content-type': 'text/json; charset=utf-8',
        mode: 'raw',
        raw: [
            { key: 'username', value: clientUser },
            { key: 'password', value: clientPassword },
            { key:'BEID', value:clientId },
            { key:'WebServicesKey', value:clientSecret }
        ]
    }
}, (err, res) => {
    console.log(" Response Section ");
});