example-rest-call-receives-auth-prompt.js

var camlQuery = '<View Scope="RecursiveAll"><RowLimit>3</RowLimit><Query><Where><Eq><FieldRef Name="FSObjType" /><Value Type="Integer">0</Value></Eq></Where></Query></View>'
return $.ajax({
    url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/Lists/GetByTitle('Documents')/GetItems?$select=ID,Title,EncodedAbsUrl,File/Name&$expand=File",
    type: "POST",
    contentType: "application/json; odata=verbose",
    headers: {
        "X-RequestDigest": $("#__REQUESTDIGEST").val(),
        "Accept": "application/json; odata=verbose"
    },
    data: JSON.stringify({
        query: {
            __metadata: {
                type: "SP.CamlQuery"
            },
            ViewXml: camlQuery,
            FolderServerRelativeUrl: '/some/folder/in/there'
        }
    })
});