How to use the saml2-js.IdentityProvider function in saml2-js

// Example use of service provider.
    // Call metadata to get XML metatadata used in configuration.
    const metadata = sp.create_metadata();

    // Initialize options object
    const idp_options = {
        sso_login_url: "https://idp.example.com/login",
        sso_logout_url: "https://idp.example.com/logout",
        certificates: [fs.readFileSync("cert-file1.crt").toString(), fs.readFileSync("cert-file2.crt").toString()],
        force_authn: true,
        sign_get_request: false,
        allow_unencrypted_assertion: false
    };

    // Call identity provider constructor with options
    const idp = new saml2.IdentityProvider(idp_options);

    // Example usage of identity provider.
    // Pass identity provider into a service provider function with options and a callback.
    sp.post_assert(idp, {}, (error: any, response: any) => {});
}


// Example: Express implementation
{
    const app = express();

    // Create service provider
    const sp_options = {
      entity_id: "https://sp.example.com/metadata.xml",
      private_key: fs.readFileSync("key-file.pem").toString(),
      certificate: fs.readFileSync("cert-file.crt").toString(),

// Create service provider
    const sp_options = {
      entity_id: "https://sp.example.com/metadata.xml",
      private_key: fs.readFileSync("key-file.pem").toString(),
      certificate: fs.readFileSync("cert-file.crt").toString(),
      assert_endpoint: "https://sp.example.com/assert"
    };
    const sp = new saml2.ServiceProvider(sp_options);

    // Create identity provider
    const idp_options = {
      sso_login_url: "https://idp.example.com/login",
      sso_logout_url: "https://idp.example.com/logout",
      certificates: [fs.readFileSync("cert-file1.crt").toString(), fs.readFileSync("cert-file2.crt").toString()]
    };
    const idp = new saml2.IdentityProvider(idp_options);

    // ------ Define express endpoints ------

    // Endpoint to retrieve metadata
    app.get("/metadata.xml", function(req, res) {
      res.type('application/xml');
      res.send(sp.create_metadata());
    });

    // Starting point for login
    app.get("/login", function(req, res) {
      sp.create_login_request_url(idp, {}, function(err, login_url, request_id) {
        if (err != null)
          return res.send(500);
        res.redirect(login_url);
      });

let lastUsed = Date.now();


		function debug(message, data) {
			ctx.app.emit('debug', {
				message: message,
				class: 'OneLoginStrategy',
				timestamp: Date.now(),
				type: 'strategy',
				data: data
			});
		}


		// instantiate the SAML identity provider
		const idp = new IdentityProvider(this.authority.details.identity_provider);

		// instantiate the SAML service provider
		const sp = new ServiceProvider({
			entity_id: ctx.request.protocol + '://' + ctx.request.host + ctx.request.path + '?metadata',
			assert_endpoint: ctx.request.protocol + '://' + ctx.request.host + ctx.request.path,
			sign_get_request: true,
			allow_unencrypted_assertion: false,
			private_key: this.authority.details.service_provider.private_key,
			certificate: this.authority.details.service_provider.certificate,
			alt_private_keys: this.authority.details.service_provider.alt_private_keys,
			alt_certs: this.authority.details.service_provider.alt_certs
		});



		// Complete Authorization Request

entity_id: "http://localhost:3000/saml/metadata",
  private_key: fs.readFileSync("certificates\\sp-cert-private.pfx").toString(),
  certificate: fs.readFileSync("certificates\\idp-cert-public.crt").toString(),
  assert_endpoint: "http://localhost:3000/saml/assert",
  allow_unencrypted_assertion: true
};
var sp = new saml2.ServiceProvider(sp_options);

// Create identity provider
// Azure AD B2C metadata:
var idp_options = {
  sso_login_url: "https://yourtenant.b2clogin.com/yourtenant.onmicrosoft.com/B2C_1A_SAML2_signup_signin/samlp/sso/login",
  sso_logout_url: "https://yourtenant.b2clogin.com/yourtenant.onmicrosoft.com/B2C_1A_SAML2_signup_signin/samlp/sso/logout",
  certificates: [fs.readFileSync("certificates\\idp-cert-public.crt").toString()]
};
var idp = new saml2.IdentityProvider(idp_options);

// ------ Define express endpoints ------

// Homepage
app.get("/", function (req, res) {
  res.send(getHTML(req.session.userName));
});

// Endpoint to retrieve metadata
app.get("/saml/metadata", function (req, res) {
  res.type('application/xml');
  res.send(sp.create_metadata());
});

// Starting point for login
app.get("/saml/login", function (req, res) {

const spOptions = {
    entity_id: process.env.ENTITY_ID,
    assert_endpoint: process.env.ASSERT_ENDPOINT,
    force_authn: false,
    nameid_format: 'urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified',
    sign_get_request: false,
    allow_unencrypted_assertion: true
  };

  const idpOptions = {
    sso_login_url: process.env.IDP_LOGIN,
    sso_logout_url: null,
    certificates: LaunchpadX509Certificate
  };

  const idp = new saml2.IdentityProvider(idpOptions);
  const sp = new saml2.ServiceProvider(spOptions);

  return { idp, sp };
};