Outlook Addin Mobile get Email as Base64

In a Mobile Outlook Addin, what is a good replacement for the unsupported (on Mobile) function Office.context.mailbox.item.getAsFileAsync?

*the function above gets the currenty open Email as base64

*no additional Microsoft Azure token-nightmares preferably

I have a working Desktop Outlook Addin that gets the Email as Base64 file via this function:

Office.context.mailbox.item.getAsFileAsync((asyncResult) => {
    if (asyncResult.status === Office.AsyncResultStatus.Failed) {
        console.log(`Error encountered during processing: ${asyncResult.error.message}`);
        return;
    }
    var emlBase64 = asyncResult.value;
});