OCSP stapling: check Content-Type. This will result in better error message in case of incorrect response from OCSP responder: ... OCSP responder sent invalid "Content-Type" header: "text/plain" while requesting certificate status, responder: ... vs. ... d2i_OCSP_RESPONSE() failed (SSL: error:0D07209B:asn1 encoding routines:ASN1_get_object:too long error:0D068066:asn1 encoding routines:ASN1_CHECK_TLEN:bad object header error:0D07803A:asn1 encoding routines:ASN1_ITEM_EX_D2I:nested asn1 error) while requesting certificate status, responder: ...