Shibboleth ACS URL mismatch with http and https - linux

Question

My ACS URL is being rewritten from https://foo.com/ to http://foo.com/ which is causing the below Exception.
Microsoft.IdentityServer.Service.Policy.PolicyServer.Engine.AssertionConsumerServiceUrlDoesNotMatchPolicyException: MSIS3200: No AssertionConsumerService is configured on the relying party trust 'foo-shibboleth-sp' that is a prefix match of the AssertionConsumerService URL 'http://foo/Shibboleth.sso/SAML2/POST' specified by the request.
The log message reflects that the auth request was sent as http as well:
<samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
AssertionConsumerServiceURL="http://foo/Shibboleth.sso/SAML2/POST"
Destination="https://bar/adfs/ls/"
ID="_12345ID" IssueInstant="2017-08-08T22:24:28Z"
ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST"
Version="2.0"><saml:Issuerxmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">foo-shibboleth-sp</saml:Issuer><samlp:NameIDPolicy AllowCreate="1"/></samlp:AuthnRequest>
2017-08-08 22:24:28 DEBUG OpenSAML.MessageEncoder.SAML2Redirect [1]: message encoded, sending redirect to client
I have included my configuration below.
The SP metadata I've configured in my IDP has the correct URL with https, but is being changed to http somewhere downstream and can be seen in the Shibboleth logs for the samlp auth request.
If I switch handlerSSL to TRUE, the ACS URL in the samlp auth request shows https. However, when it's set to TRUE, anything at the path of /Shibboleth.sso/ such as /Status, or /SAML2/POST are 404ing.
I should also note that this is actually a site migration and this was all on windows in a datacenter now it's on Linux in AWS. There could be an issue with the Load Balancer where we terminate SSL, but haven't been able to debug that.
In the SP metadata that was provided to the IDP, I specify the https /SAML2/POST url. There is a bunch of config here, but I tried to highlight the relevant stuff.
<md:EntityDescriptor xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata" ID="_97e389f1c212...." entityID="foo-shibboleth-sp">
...
<init:RequestInitiator xmlns:init="urn:oasis:names:tc:SAML:profiles:SSO:request-init" Binding="urn:oasis:names:tc:SAML:profiles:SSO:request-init" Location="https://foo/Shibboleth.sso/Login"/>
....
<md:AssertionConsumerService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://foo/Shibboleth.sso/SAML2/POST" index="10"/>
Then, in the shibboleth2.xml on my SP, I have the following application override config:
<ApplicationOverride id="lms" entityID="foo-shibboleth-sp"
homeURL="/path/to/sso/location">
<Sessions lifetime="28800" timeout="3600" checkAddress="false"
handlerURL="/Shibboleth.sso" handlerSSL="false"
exportLocation="https://foo/Shibboleth.sso/GetAssertion" exportACL="127.0.0.1"
idpHistory="false" idpHistoryDays="7">
<!-- Default example directs to a specific IdP's SSO service (favoring SAML 2 over Shib 1). -->
<SessionInitiator type="Chaining" Location="/Login" isDefault="true" id="Intranet"
relayState="cookie" entityID="http://bar/adfs/services/trust">
<SessionInitiator type="SAML2" acsIndex="1" template="bindingTemplate.html"/>
<SessionInitiator type="Shib1" acsIndex="5"/>
</SessionInitiator>
</Sessions>
<MetadataProvider type="XML" file="/etc/shibboleth/metadata-sp.xml"/>
<!-- Map to extract attributes from SAML assertions. -->
<AttributeExtractor type="XML" validate="true" path="/etc/shibboleth/attribute-map.xml"/>
</ApplicationOverride>
Finally, the only other piece that I have determined could be causing issues, is the IDP metadata here:
<EntityDescriptor xmlns="urn:oasis:names:tc:SAML:2.0:metadata" ID="_1234-..." entityID="http://bar/adfs/services/trust">
...
<AssertionConsumerService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://bar/adfs/ls/" index="0" isDefault="true" />
....
<SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect" Location="https://bar/adfs/ls/" />
<SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://bar/adfs/ls/" />
apache config also, though it seems pretty cookie-cutter
<Location />
ShibRequestSetting applicationId lms
</Location>
<Location /path/to/sso/location>
ShibRequestSetting applicationId lms
AuthType shibboleth
ShibRequestSetting requireSession 1
require valid-user
</Location>

Answer 1

The problem ended up being related to SSL Offload with the AWS Load Balancer. Because we were terminating at the ELB, we needed to set https:// on the ServerName directive in Apache config so that it would generate the https self-referential urls.
http://httpd.apache.org/docs/2.2/mod/core.html#servername