The following information can be obtained with Wireshark or with Noodle DEBUG;

https://intranet.onelogin.com/trust/saml2/http-post/sso/699546?SAMLRequest=fVLLbtsw...%2FkD&RelayState=https%3A%2F%2Fintra.net%2FSAML.po

Should be sent to the IdP which before it is deflated and base 64 encoded looks like

<samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" ID="-5abe3a1a-1671d27aa18--8000" Version="2.0" IssueInstant="2018-11-16T15:33:17Z" ProviderName="Noodle" Destination="https://intranet.onelogin.com/trust/saml2/http-post/sso/699546" ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" AssertionConsumerServiceURL="https://intra.net/SAML.po">
    <saml:Issuer>Noodle</saml:Issuer>
    <samlp:NameIDPolicy Format="urn:oasis:names:tc:SAML:2.0:nameid-format:encrypted" AllowCreate="true" />
    <samlp:RequestedAuthnContext Comparison="false">
        <saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml:AuthnContextClassRef>
    </samlp:RequestedAuthnContext>
</samlp:AuthnRequest>

The IdP should reply with "Content-Type: application/x-www-form-urlencoded" containing "SAMLResponse: PHN...fCg==" which when base 64 decoded looks like

<samlp:Response xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" ID="R6229535893ec8f41746de8cd0bb42fe1008d88a7" Version="2.0" IssueInstant="2018-11-16T15:33:18Z" Destination="{recipient}" InResponseTo="-5abe3a1a-1671d27aa18--8000">
    <saml:Issuer>https://app.onelogin.com/saml/metadata/699546</saml:Issuer>
    <samlp:Status>
        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success" />
    </samlp:Status>
    <saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Version="2.0" ID="pfx95004805-783d-f0ee-f32d-17d50ca7ef90" IssueInstant="2018-11-16T15:33:18Z">
        <saml:Issuer>https://app.onelogin.com/saml/metadata/699546</saml:Issuer>
        <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
            <ds:SignedInfo>
                <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
                <ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" />
                <ds:Reference URI="#pfx95004805-783d-f0ee-f32d-17d50ca7ef90">
                    <ds:Transforms>
                        <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
                        <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
                    </ds:Transforms>
                    <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
                    <ds:DigestValue>uCsDHp/wXNnMIz7nkq2D7OF81zY=</ds:DigestValue>
                </ds:Reference>
            </ds:SignedInfo>
            <ds:SignatureValue>QbDsbkTMULdxYmiV8lu64jUE4BNj7ETQvUhjlgHrbaUKMaUdnluJma8T9jh8WOUEQw+Of/MGP4hMJE18f2XOJJK3X3VQnlggE5z98xjHrP0SugRH+elgQpOVkB9ht685UXtzRF6SVAIwstOGphOgqgGRwrG9fPQpN6DAKr00IOc6ItM7cbhVnA+EA8iHP8WP0n+VZXkdub9Sb/tgVkimih3/7DZPIWi6FpmlsTN88mlxBXJKnslr1Iw0ZLqLjR5dJSFz7SHrkBijirFf/kOydoQeOQrRS+6XzOmXayWCP2hHWXVvr5Ye1GbDZyjKTxMpObc+Lv6nj7llC1Mal2M0cw==</ds:SignatureValue>
            <ds:KeyInfo>
                <ds:X509Data>
                    <ds:X509Certificate>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</ds:X509Certificate>
                </ds:X509Data>
            </ds:KeyInfo>
        </ds:Signature>
        <saml:Subject>
            <saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress">tim@intra.net</saml:NameID>
            <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
                <saml:SubjectConfirmationData NotOnOrAfter="2018-11-16T15:36:18Z" Recipient="{recipient}" InResponseTo="-5abe3a1a-1671d27aa18--8000" />
            </saml:SubjectConfirmation>
        </saml:Subject>
        <saml:Conditions NotBefore="2018-11-16T15:30:18Z" NotOnOrAfter="2018-11-16T15:36:18Z">
            <saml:AudienceRestriction>
                <saml:Audience>{audience}</saml:Audience>
            </saml:AudienceRestriction>
        </saml:Conditions>
        <saml:AuthnStatement AuthnInstant="2018-11-16T15:33:17Z" SessionNotOnOrAfter="2018-11-17T15:33:18Z" SessionIndex="_c9a77760-cbdb-0136-fc65-0233ce1b6e10">
            <saml:AuthnContext>
                <saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml:AuthnContextClassRef>
            </saml:AuthnContext>
        </saml:AuthnStatement>
    </saml:Assertion>
</samlp:Response>