http: introduce AWS HTTP v4 Signature

It is a security process for HTTP.

It doesn't seems to be standard, but it is used by some cloud providers.

Aws:
https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html
Outscale:
https://wiki.outscale.net/display/EN/Creating+a+Canonical+Request
GCP (I didn't test that this code work with GCP though):
https://cloud.google.com/storage/docs/access-control/signing-urls-manually

most of the code is in lib/http_v4_signature.c

Information require by the algorithm:
- The URL
- Current time
-  some prefix that are append to some of the signature parameters.

The data extracted from the URL are: the URI, the region,
the host and the API type

example:
https://api.eu-west-2.outscale.com/api/latest/ReadNets
        ~~~ ~~~~~~~~               ~~~~~~~~~~~~~~~~~~~
        ^       ^                          ^
       /         \                        URI
   API type     region

Small description of the algorithm:
- make canonical header using content type, the host, and the date
- hash the post data
- make canonical_request using custom request, the URI,
  the get data, the canonical header, the signed header
  and post data hash
- hash canonical_request
- make str_to_sign using one of the prefix pass in parameter,
  the date, the credential scope and the canonical_request hash
- compute hmac from date, using secret key as key.
- compute hmac from region, using above hmac as key
- compute hmac from api_type, using above hmac as key
- compute hmac from request_type, using above hmac as key
- compute hmac from str_to_sign using above hmac as key
- create Authorization header using above hmac, prefix pass in parameter,
  the date, and above hash

Signed-off-by: Matthias Gatto <matthias.gatto@outscale.com>

Closes #5703

include/curl/curl.h

@@ -787,6 +787,7 @@ typedef enum {
 #define CURLAUTH_DIGEST_IE    (((unsigned long)1)<<4)
 #define CURLAUTH_NTLM_WB      (((unsigned long)1)<<5)
 #define CURLAUTH_BEARER       (((unsigned long)1)<<6)
+#define CURLAUTH_AWS_SIGV4 (((unsigned long)1)<<7)
 #define CURLAUTH_ONLY         (((unsigned long)1)<<31)
 #define CURLAUTH_ANY          (~CURLAUTH_DIGEST_IE)
 #define CURLAUTH_ANYSAFE      (~(CURLAUTH_BASIC|CURLAUTH_DIGEST_IE))
@@ -2073,6 +2074,9 @@ typedef enum {
   CURLOPT(CURLOPT_HSTSWRITEFUNCTION, CURLOPTTYPE_FUNCTIONPOINT, 303),
   CURLOPT(CURLOPT_HSTSWRITEDATA, CURLOPTTYPE_CBPOINT, 304),
 
+  /* Provider for V4 signature */
+  CURLOPT(CURLOPT_AWS_SIGV4, CURLOPTTYPE_STRINGPOINT, 305),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;