Token endpoint does not support Expect 100-continue HTTP header

[fujie]

While integrating my existing OIDC relying party, the relying party library pre-sends expect header to the world ID's token endpoint. But the token endpoint does not support expect header and return error 'Error: Cannot remove headers after they are sent to the client'. I guess this issue is not directly related to the idkit itself, but I wish Worldcoin to fix this.