I see in the documentation that ProviderName is an optional value used to specify a friendly name when issuing an AuthnRequest. When acting as an IdP and receiving an AuthnRequest from a SP, if an AuthnRequest does not contain a saml:Issuer value, is the ProviderName used by ComponentSpace to match to a SP within the configuration with the maching ProviderName if one is set?

We expect the Issuer field to always be present and use this to determine the partner SP. If the issuer field isn’t present then this is considered an error. We don’t use the ProviderName.

How can the provider name be obtained? Would one simply get the SP entity id returned via the receive sso call, then look in the config and get the provider name?

Use one of the SAMLIdentityProvider.ReceiveSSO methods that returns SSOOptions. The SSOOptions includes a ProviderName property which is the provider name from the authn request.