src/Certificate/BaseCertificateProvider.php
public function getCertificateFromUri($certificateChainUri)
    {
        $certificateChain = $this->retrieveCertificateFromStore($certificateChainUri);

        if (!is_null($certificateChain) || $certificateChain === false) {
            $parsedCertificate = $this->parseCertificate($certificateChain);
            if (!$this->validateCertificateDate($parsedCertificate) || !$this->verifyCertificateSubjectAltNamePresent($parsedCertificate)) {
                $certificateChain = $this->storeRemoteCertificate($certificateChainUri);
            }
        } else {
            $certificateChain = $this->storeRemoteCertificate($certificateChainUri);
        }

        return $certificateChain;
    }
public function getCertificateFromUri($certificateChainUri)
    {
        $certificateChain = $this->retrieveCertificateFromStore($certificateChainUri);

        if (!is_null($certificateChain) || $certificateChain === false) {
            $parsedCertificate = $this->parseCertificate($certificateChain);
            if (!$this->validateCertificateDate($parsedCertificate) || !$this->verifyCertificateSubjectAltNamePresent($parsedCertificate)) {
                $certificateChain = $this->storeRemoteCertificate($certificateChainUri);
            }
        } else {
            $certificateChain = $this->storeRemoteCertificate($certificateChainUri);
        }

        return $certificateChain;
    }
Download/retrieve the certificate chain from a given location

@param string $certificateChainUri

@return string|null