SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://www.progress.com/documentation/sitefinity-cms/authenticate

SfSdkOpenId.js

function loginOpenId(sitefinity, sitefinityUrl, username, password) {
    var url = sitefinityUrl + "/Sitefinity/Authenticate/OpenID/connect/token";
    var data = {
        username: username,
        password: password,
        grant_type: "password",
        scope: "openid",
        client_id: "testApp",
        client_secret: "secret"
    };

    var body = "";
    Object.keys(data).forEach(key => {
        if (body.length) {
            body += "&";
        }
        body += key + "=";
        body += encodeURIComponent(data[key]);
    });

    var xhr = new XMLHttpRequest();

    xhr.open("POST", url, true);
    xhr.addEventListener("load", () => {
        if (xhr.status == 200) {
            let token = JSON.parse(xhr.responseText);

            let tokenObj = {
                type: token.token_type,
                value: token.access_token
            };

            sitefinity.authentication.setToken(tokenObj);
        }
    });

    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

    xhr.send(body);
}