証明書ファイルのMIMEタイプまとめ
application/pkcs8 .p8 .key
application/pkcs10 .p10 .csr
application/pkix-cert .cer
application/pkix-crl .crl
application/pkcs7-mime .p7c
application/x-x509-ca-cert .crt .der
application/x-x509-user-cert .crt
application/x-pkcs7-crl .crl
application/x-pem-file .pem
application/x-pkcs12 .p12 .pfx
application/x-pkcs7-certificates .p7b .spc
application/x-pkcs7-certreqresp .p7r
参考URL: https://pki-tutorial.readthedocs.io/en/latest/mime.html