[Project] Start working on AWS Lua API

diff --git a/lualib/lua_aws.lua b/lualib/lua_aws.lua
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+++ b/lualib/lua_aws.lua
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+--[[
+Copyright (c) 2021, Vsevolod Stakhov <vsevolod@highsecure.ru>
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+]]--
+
+
+--[[[
+-- @module lua_aws
+-- This module contains Amazon AWS utility functions
+--]]
+
+local N = "aws"
+local rspamd_logger = require "rspamd_logger"
+local lua_util = require "lua_util"
+local rspamd_crypto_hash = require "rspamd_cryptobox_hash"
+
+local exports = {}
+
+-- Returns a canonical representation of today date
+local function today_canonical()
+  return os.date('!%Y%m%d', os.time())
+end
+
+--[[[
+-- @function lua_aws.aws_date([date_str])
+-- Returns an aws date header corresponding to the specific date
+--]]
+local function aws_date(date_str)
+  if not date_str then
+    date_str = today_canonical()
+  end
+
+  return date_str .. 'T000000Z'
+end
+
+exports.aws_date = aws_date
+
+
+-- Local cache of the keys to save resources
+local cached_keys = {}
+
+local function maybe_get_cached_key(date_str, secret_key, region, service, req_type)
+  local bucket = cached_keys[tonumber(date_str)]
+
+  if not bucket then
+    return nil
+  end
+
+  local elt = bucket[string.format('%s.%s.%s.%s', secret_key, region, service, req_type)]
+  if elt then
+    return elt
+  end
+end
+
+local function save_cached_key(date_str, secret_key, region, service, req_type, key)
+  local numdate = tonumber(date_str)
+  -- expire old buckets
+  for k,_ in pairs(cached_keys) do
+    if k < numdate then
+      cached_keys[k] = nil
+    end
+  end
+
+
+  local bucket = cached_keys[tonumber(date_str)]
+  local idx = string.format('%s.%s.%s.%s', secret_key, region, service, req_type)
+
+  if not bucket then
+    cached_keys[tonumber(date_str)] = {
+      idx = key
+    }
+  else
+    bucket[idx] = key
+  end
+end
+--[[[
+-- @function lua_aws.aws_signing_key([date_str], secret_key, region, [service='s3'], [req_type='aws4_request'])
+-- Returns a signing key for the specific parameters
+--]]
+local function aws_signing_key(date_str, secret_key, region, service, req_type)
+  if not date_str then
+    date_str = today_canonical()
+  end
+
+  if not service then
+    service = 's3'
+  end
+
+  if not req_type then
+    req_type = 'aws4_request'
+  end
+
+  assert(type(secret_key) == 'string')
+  assert(type(region) == 'string')
+
+  local maybe_cached = maybe_get_cached_key(date_str, secret_key, region, service, req_type)
+
+  if maybe_cached then
+    return maybe_cached
+  end
+
+  local hmac1 = rspamd_crypto_hash.create_specific_keyed("AWS4" .. secret_key, "sha256", date_str):bin()
+  local hmac2 = rspamd_crypto_hash.create_specific_keyed(hmac1, "sha256", date_str):bin()
+  local hmac3 = rspamd_crypto_hash.create_specific_keyed(hmac2, "sha256",region):bin()
+  local hmac4 = rspamd_crypto_hash.create_specific_keyed(hmac3, "sha256", service):bin()
+  local final_key = rspamd_crypto_hash.create_specific_keyed(hmac4, "sha256", req_type):bin()
+
+  save_cached_key(date_str, secret_key, region, service, req_type, final_key)
+
+  return final_key
+end
+
+exports.aws_signing_key = aws_signing_key
+
+return exports