Is your feature request related to a problem? Please describe.

I'm using node-saml as part of my Remix web stack. However, I don't want to directly use the getAuthorizeFormAsync as it means I can't customise the form at all and just generally makes working with the library more difficult then I feel it needs to be.

Describe the solution you'd like

A getSAMLRequestValue (or similarly named) method on the main SAML class that I can use to generate the Base64 encoded SAMLRequest value, to pass into my own form.

Describe alternatives you've considered

I'm doing the following as a workaround currently which works but isn't ideal:

 const authForm = await saml.getAuthorizeFormAsync("");
  // Extract the SAMLRequest value with regex
  const SAMLRequestValue = authForm
    .split(`name="SAMLRequest" value="`)[1]
    .split(`"`)[0];

I would love to contribute to the library and if I can I'll get a PR raised to propose a solution.