Update OpenSSL Impelementation to Address Review Comments.

Added documentation to clarify each step of the implementation.

src/crypto/CHIPCryptoPALOpenSSL.cpp

@@ -1990,6 +1990,10 @@ CHIP_ERROR ExtractCRLDistributionPointURIFromX509Cert(const ByteSpan & certifica
     x509certificate = d2i_X509(nullptr, ppCertificate, static_cast<long>(certificate.size()));
     VerifyOrExit(x509certificate != nullptr, err = CHIP_ERROR_NO_MEMORY);
 
+    // CRL Distribution Point Extension is encoded as a secuense of DistributionPoint:
+    //     CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
+    //
+    // This implementation only supports a single DistributionPoint (sequence of size 1)
     crldp =
         reinterpret_cast<STACK_OF(DIST_POINT) *>(X509_get_ext_d2i(x509certificate, NID_crl_distribution_points, nullptr, nullptr));
     VerifyOrExit(crldp != nullptr, err = CHIP_ERROR_NOT_FOUND);
@@ -1999,21 +2003,46 @@ CHIP_ERROR ExtractCRLDistributionPointURIFromX509Cert(const ByteSpan & certifica
     VerifyOrExit(dp != nullptr, err = CHIP_ERROR_NOT_FOUND);
     VerifyOrExit(dp->distpoint != nullptr && dp->distpoint->type == 0, err = CHIP_ERROR_NOT_FOUND);
 
+    // The DistributionPoint is a sequence of three optional elements:
+    //     DistributionPoint ::= SEQUENCE {
+    //         distributionPoint       [0]     DistributionPointName OPTIONAL,
+    //         reasons                 [1]     ReasonFlags OPTIONAL,
+    //         cRLIssuer               [2]     GeneralNames OPTIONAL }
+    //
+    // where the DistributionPointName is a CHOICE of:
+    //     DistributionPointName ::= CHOICE {
+    //         fullName                [0]     GeneralNames,
+    //         nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }
+    //
+    // The URI should be encoded in the fullName element.
+    // This implementation only supports a single GeneralName in the fullName sequence:
+    //     GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
     gens = dp->distpoint->name.fullname;
     VerifyOrExit(sk_GENERAL_NAME_num(gens) == 1, err = CHIP_ERROR_NOT_FOUND);
 
+    // The CDP URI is encoded as a uniformResourceIdentifier field of the GeneralName:
+    //     GeneralName ::= CHOICE {
+    //         otherName                       [0]     OtherName,
+    //         rfc822Name                      [1]     IA5String,
+    //         dNSName                         [2]     IA5String,
+    //         x400Address                     [3]     ORAddress,
+    //         directoryName                   [4]     Name,
+    //         ediPartyName                    [5]     EDIPartyName,
+    //         uniformResourceIdentifier       [6]     IA5String,
+    //         iPAddress                       [7]     OCTET STRING,
+    //         registeredID                    [8]     OBJECT IDENTIFIER }
     gen = sk_GENERAL_NAME_value(gens, 0);
     VerifyOrExit(gen->type == GEN_URI, err = CHIP_ERROR_NOT_FOUND);
 
     uri    = reinterpret_cast<ASN1_STRING *>(GENERAL_NAME_get0_value(gen, nullptr));
     urlptr = reinterpret_cast<const char *>(ASN1_STRING_get0_data(uri));
-    len    = strlen(urlptr);
+    len    = ASN1_STRING_length(uri);
     VerifyOrExit(
         (len > strlen(kValidCDPURIHttpPrefix) && strncmp(urlptr, kValidCDPURIHttpPrefix, strlen(kValidCDPURIHttpPrefix)) == 0) ||
             (len > strlen(kValidCDPURIHttpsPrefix) &&
              strncmp(urlptr, kValidCDPURIHttpsPrefix, strlen(kValidCDPURIHttpsPrefix)) == 0),
         err = CHIP_ERROR_NOT_FOUND);
-    err = CopyCharSpanToMutableCharSpan(CharSpan::fromCharString(urlptr), cdpurl);
+    err = CopyCharSpanToMutableCharSpan(CharSpan(urlptr, len), cdpurl);
 
 exit:
     sk_DIST_POINT_pop_free(crldp, DIST_POINT_free);