Allow Cast certificates to have serial numbers greater than 20 bytes.

net/cert/internal/parse_certificate.h

Index: net/cert/internal/parse_certificate.h
diff --git a/net/cert/internal/parse_certificate.h b/net/cert/internal/parse_certificate.h
index 6fde44821c27bf86c7e7c9e1a0db7305d809beb1..13409dc3be54896d4287629f933a9be90d269e5c 100644
--- a/net/cert/internal/parse_certificate.h
+++ b/net/cert/internal/parse_certificate.h
@@ -46,6 +46,14 @@ struct ParsedTbsCertificate;
 //     gracefully handle such certificates.
 NET_EXPORT bool VerifySerialNumber(const der::Input& value) WARN_UNUSED_RESULT;
 
+struct NET_EXPORT ParseCertificateOptions {
+  // If set to true, then parsing will skip checks on the certificate's serial
+  // number. The only requirement will be that the serial number is an INTEGER,
+  // however it is not required to be a valid DER-encoding (i.e. minimal
+  // encoding), nor is it required to be constrained to any particular length.
+  bool allow_invalid_serial_numbers = false;
+};
+
 // Parses a DER-encoded "Certificate" as specified by RFC 5280. Returns true on
 // success and sets the results in the |out_*| parameters.
 //
@@ -87,7 +95,8 @@ NET_EXPORT bool ParseCertificate(const der::Input& certificate_tlv,
     WARN_UNUSED_RESULT;
 
 // Parses a DER-encoded "TBSCertificate" as specified by RFC 5280. Returns true
-// on success and sets the results in |out|.
+// on success and sets the results in |out|. Certain invalid inputs may
+// be accepted based on the provided |options|.
 //
 // Note that on success |out| aliases data from the input |tbs_tlv|.
 // Hence the fields of the ParsedTbsCertificate are only valid as long as
@@ -115,6 +124,7 @@ NET_EXPORT bool ParseCertificate(const der::Input& certificate_tlv,
 //                                 -- If present, version MUST be v3
 //            }
 NET_EXPORT bool ParseTbsCertificate(const der::Input& tbs_tlv,
+                                    const ParseCertificateOptions& options,
                                     ParsedTbsCertificate* out)
     WARN_UNUSED_RESULT;
 
@@ -149,7 +159,13 @@ struct NET_EXPORT ParsedTbsCertificate {
   // instance if the serial number was 1000 then this would contain bytes
   // {0x03, 0xE8}.
   //
-  // In addition to being a valid DER-encoded INTEGER, parsing guarantees that
+  // The serial number may or may not be a valid DER-encoded INTEGER:
+  //
+  // If the option |allow_invalid_serial_numbers=true| was used during
+  // parsing, then nothing further can be assumed about these bytes.
+  //
+  // Otherwise if |allow_invalid_serial_numbers=false| then in addition
+  // to being a valid DER-encoded INTEGER, parsing guarantees that
   // the serial number is at most 20 bytes long. Parsing does NOT guarantee
   // that the integer is positive (might be zero or negative).
   der::Input serial_number;