Подключение корневых сертификатов в nginx
ssl_trusted_certificate /etc/nginx/cert/trustchain.crt;
Comodo (PositiveSSL)
cat COMODORSADomainValidationSecureServerCA.crt COMODORSAAddTrustCA.crt AddTrustExternalCARoot.crt > comodo.pem
GeoTrust (RapidSSL)
cat www.youdomain.com.p7b www.youdomain.com.ca-bundle > geotrust.pem