Browser/Artifact handler does not support HTTP method (POST)

Somehow, the IdP send a POST profile to your SP's artifact handler. POST profile is the default "response" protocol from IdP. If the IdP cannot identify the SP, it will response back using POST despite the SP may have requested through Artifact. IdP may not be able to identify the SP, however, the SP may satisfy one of IdP's defaultRelyingParty configuration, hence the IdP will try its best to communicate back to the SP, through its default protocol -- POST profile.

Check that:

• SP is configured to use Artifact and this is the one being registered in the metadata as its default protocol
• check SP's providerId declaration against metadata
• make sure IdP accepts this SP on its RelyingParty^? or defaultRelyingParty
• check IdP log to see if it can identify this SP (i.e. no "No metadata found for provider..." error on its log)