How to add `<Extensions>` element in SAML request using passport-saml?

Question

I am using passport-saml as a SAML client and requesting to external IDP. I want to add <Extensions> element in SAML request like below:

<samlp:AuthnRequest AssertionConsumerServiceURL="https://iam.test.fi/oxauth/postlogin" Destination="https://testidp.fi/idp/profile/SAML2/Redirect/SSO" ID="_3a5525fc-f5cc-46af-add6-70bbc27ecebf" IssueInstant="2021-05-19T11:05:04Z" Version="2.0" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">
<saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">https://iam.test.fi/oxauth/1</saml:Issuer>

<samlp:Extensions>
<vetuma xmlns="urn:vetuma:SAML:2.0:extensions"><test>fi</test></vetuma>
</samlp:Extensions>

<samlp:NameIDPolicy AllowCreate="true"/>
<samlp:RequestedAuthnContext Comparison="exact">
<saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">http://testidp.fi/2017/loa3</saml:AuthnContextClassRef>
</samlp:AuthnRequest>

I checked passport-saml config parameters but didn't find any one which gives facility to add <Exntesions> element.

Thank you.