How to retrieve Okta SAML token from Okta web API programmatically

I am taking this answer as base for my question because I was nearly there...

I am building a proxy that would convert Okta SAML into our own JWT. Idea is - take SAML token and use it to make our private JWT with claims. The setup is JS UI - .net WEB API - Okta SSO

From .net web API I've successfully connected to Okta and got token using POST payload

{
  "username": "myuser@company.com",
  "password": "mysecret",
  "options": {
    "multiOptionalFactorEnroll": false,
    "warnBeforePasswordExpired": false
  }
}

Then I've retrieved the one-time token (cookie token) from the response using POST on https://SomeCompany.okta.com/api/v1/sessions?additionalFields=cookieToken with payload

{ "sessionToken": "token I retrieved in the step 1" }

And this ^^ gave me the response which contains the cookieToken. And now I used this cookie token to make a GET request to the URL set in my Okta application, which looks like https://SomeCompany.okta.com/app/SomeCompanysso_123/4tg7uknm765on6yhnmk/sso/saml

I added a query parameter so it looks like https://SomeCompany.okta.com/app/SomeCompanysso_123/4tg7uknm765on6yhnmk/sso/saml?onetimetoken=THE_TOKEN_I_GOT_IN_STEP2

And this fetched me the whole SSO HTML page with SAML token in the hidden field SAMLResponse.

Is there a way to get this SAMLResponse cleanly, without need to rip it out of HTML and if not, what is the efficient way to do it?

Thanks

Based on the question, this is the answer to the last part for the obtaining of SAML token cleanly. We retrieve the HTML Document, load it into the c# instance and take the SAML token node for further processing.

// token comes in the controle with this name
private const string _samlTokenFormControlName = "SAMLResponse";

// here response content 'string responseContent' is HTML page
var htmlDoc = new HtmlDocument();
try
{
    htmlDoc.LoadHtml(responseContent);
    HtmlNodeCollection nodes =
    htmlDoc.DocumentNode.SelectNodes($"//input[@name='{_samlTokenFormControlName}']");
    if (nodes.Count > 0)
    {
        samlToken = nodes[0].GetAttributeValue("value", null);
        if (samlToken != null)
            retVal = true;
        }
}
catch
{}

return retVal; // gets me clean SAML token

After this I decode this token and retrieve Claims out of it using Microsoft.IdentityModel.Tokens.Saml2.