Burrego: implement missing builtins

[ereslibre]

Relation of builtin-list and builtin-usage in different repositories containing builtins, so we can prioritize builtin implementation depending on the usage. The list of the full SDK-dependant bultins follows:

Category	Built-in	Status
Numbers	rand.intn	-
Objects	json.patch	Implemented
Strings	sprintf	Implemented
Regex	regex.split	-
	regex.globs_match	-
	regex.template_match	-
	regex.find_n	-
Glob	glob.quote_meta	Implemented
Units	units.parse_bytes	-
Encoding	base64url.encode_no_pad	Implemented
	urlquery.encode	Implemented
	urlquery.encode_object	Implemented
	urlquery.decode	Implemented
	urlquery.decode_object	Implemented
	json.is_valid	Implemented
	yaml.marshal	Implemented
	yaml.unmarshal	Implemented
	yaml.is_valid	Implemented
	hex.encode	Implemented
	hex.decode	Implemented
Token Signing	io.jwt.encode_sign_raw	-
	io.jwt.encode_sign	-
Token Verification	io.jwt.verify_rs256	-
	io.jwt.verify_rs384	-
	io.jwt.verify_rs512	-
	io.jwt.verify_ps256	-
	io.jwt.verify_ps384	-
	io.jwt.verify_ps512	-
	io.jwt.verify_es256	-
	io.jwt.verify_es384	-
	io.jwt.verify_es512	-
	io.jwt.verify_hs256	-
	io.jwt.verify_hs384	-
	io.jwt.verify_hs512	-
	io.jwt.decode	-
	io.jwt.decode_verify	-
Time	time.now_ns	Implemented
	time.parse_ns	-
	time.parse_rfc3339_ns	Implemented
	time.parse_duration_ns	-
	time.date	Implemented
	time.clock	-
	time.weekday	-
	time.add_date	-
	time.diff	-
Cryptography	crypto.x509.parse_certificates	-
	crypto.x509.parse_and_verify_certificates	-
	crypto.x509.parse_certificate_request	-
	crypto.md5	-
	crypto.sha1	-
	crypto.sha256	-
HTTP	http.send	-
Net	net.cidr_contains_matches	-
	net.cidr_expand	-
	net.cidr_merge	-
UUID	uuid.rfc4122	-
Semantic Versions	semver.is_valid	Implemented
	semver.compare	Implemented
Rego	rego.parse_module	-
OPA	opa.runtime	-
Debugging	trace	Implemented

The use of builtins, per repo:

• Gatekeeper library (https://github.com/open-policy-agent/gatekeeper-library)

  • re_match: now renamed to regex.match, but not updated in the policy code. 12 usages.
  • trace: only used in tests. 18 usages.

• OPA library (https://github.com/open-policy-agent/library/tree/master/kubernetes)

  • re_match: now renamed to regex.match, but not updated in the policy code. 3 usages.
  • yaml.unmarshal: 1 usage.
  • http.send: 1 usage. I don't think we should aim for this right now.
  • trace: only used in tests. 9 usages.

The rest of the table is not used by the policies in the mentioned repositories.