/usr/include/saml/saml2/ is in libsaml2-dev 2.5.3-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/saml/saml2/binding/
/usr/include/saml/saml2/binding/SAML2Artifact.h
/usr/include/saml/saml2/binding/SAML2ArtifactType0004.h
/usr/include/saml/saml2/binding/SAML2MessageDecoder.h
/usr/include/saml/saml2/binding/SAML2Redirect.h
/usr/include/saml/saml2/binding/SAML2SOAPClient.h
/usr/include/saml/saml2/core/
/usr/include/saml/saml2/core/Assertions.h
/usr/include/saml/saml2/core/Protocols.h
/usr/include/saml/saml2/metadata/
/usr/include/saml/saml2/metadata/AbstractMetadataProvider.h
/usr/include/saml/saml2/metadata/DiscoverableMetadataProvider.h
/usr/include/saml/saml2/metadata/DynamicMetadataProvider.h
/usr/include/saml/saml2/metadata/EndpointManager.h
/usr/include/saml/saml2/metadata/EntityMatcher.h
/usr/include/saml/saml2/metadata/Metadata.h
/usr/include/saml/saml2/metadata/MetadataCredentialContext.h
/usr/include/saml/saml2/metadata/MetadataCredentialCriteria.h
/usr/include/saml/saml2/metadata/MetadataFilter.h
/usr/include/saml/saml2/metadata/MetadataProvider.h
/usr/include/saml/saml2/metadata/ObservableMetadataProvider.h
/usr/include/saml/saml2/profile/
/usr/include/saml/saml2/profile/AssertionValidator.h
/usr/include/saml/saml2/profile/BrowserSSOProfileValidator.h
/usr/include/saml/saml2/profile/SAML2AssertionPolicy.h