Adds support for intermediate certificates in PDF document signing

[felixble]

Implements the ability to include intermediate certificates for establishing the trust chain when signing PDF documents. Supports the default behaviour of *.p12 files containing intermediate certificates in extracerts attribute.

I had the following files:

• certificate.cer - my certificate
• private.key - private key for the certificate
• intermediate.cer - intermediate certificate needed for establishing the trust chain to the trusted root certificate

I created a p12 file with the following command:

openssl pkcs12 -export -out your_combined_cert.p12 -inkey private.key -in certificate.cer -certfile intermediate.cer

When reading the p12 file the array stored PDFDoc::$_certificate contains an additional attribute extracerts which contains the intermediate certificate.

With these changes the extracerts will be taken into account.

[dealfonso]

Hi,

thank you for your help... I'll check this PR.

[dealfonso]

the new TSA and LTV support in PR #70 makes new changes that include the intermediate certificates