Sending XML header with SimpleSamlPhp

I'm using SimpleSamlPhp for SAML Service Provider.

SimpleSamlPhp is sending sending auth request without xml headers, but IdP says they require an xml header. How can I add utf-8 header to request? (<?xml version="1.0" encoding="UTF-8"?>)

This is how I send

<samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" ID="gfpdfaailecofabshsehljipgpofofghjjahggi" Version="2.0" IssueInstant="2011-08-23T06:26:06Z" ProtocolBinding="urn:oasis: etc.....

This is how IdP asks for

<?xml version="1.0" encoding="UTF-8"?><samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" ID="gfpdfaailecofabshsehljipgpofofghjjahggi" Version="2.0" IssueInstant="2011-08-23T06:26:06Z" ProtocolBinding="urn:oasis: etc.....

PS: Tested my SP on Feide OpenIdp and works fi开发者_如何学Cne.