class Gem::S3URISigner

S3URISigner implements AWS SigV4 for S3 Source to avoid a dependency on the aws-sdk-* gems More on AWS SigV4: docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-authenticating-requests.html

Constants

BASE64_URI_TRANSLATE
EC2_METADATA_CREDENTIALS
S3Config

Attributes

uri[RW]

Public Class Methods

new(uri) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 36
def initialize(uri)
  @uri = uri
end

Public Instance Methods

sign(expiration = 86400) click to toggle source

Signs S3 URI using query-params according to the reference: docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html

# File lib/rubygems/s3_uri_signer.rb, line 42
def sign(expiration = 86400)
  s3_config = fetch_s3_config

  current_time = Time.now.utc
  date_time = current_time.strftime("%Y%m%dT%H%m%SZ")
  date = date_time[0,8]

  credential_info = "#{date}/#{s3_config.region}/s3/aws4_request"
  canonical_host = "#{uri.host}.s3.#{s3_config.region}.amazonaws.com"

  query_params = generate_canonical_query_params(s3_config, date_time, credential_info, expiration)
  canonical_request = generate_canonical_request(canonical_host, query_params)
  string_to_sign = generate_string_to_sign(date_time, credential_info, canonical_request)
  signature = generate_signature(s3_config, date, string_to_sign)

  URI.parse("https://#{canonical_host}#{uri.path}?#{query_params}&X-Amz-Signature=#{signature}")
end

Private Instance Methods

base64_uri_escape(str) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 143
def base64_uri_escape(str)
  str.gsub(/[\+\/=\n]/, BASE64_URI_TRANSLATE)
end
create_request_pool(uri) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 166
def create_request_pool(uri)
  proxy_uri = Gem::Request.proxy_uri(Gem::Request.get_proxy_from_env(uri.scheme))
  certs = Gem::Request.get_cert_files
  Gem::Request::ConnectionPools.new(proxy_uri, certs).pool_for(uri)
end
ec2_metadata_credentials_json() click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 147
def ec2_metadata_credentials_json
  require 'net/http'
  require 'rubygems/request'
  require 'rubygems/request/connection_pools'
  require 'json'

  metadata_uri = URI(EC2_METADATA_CREDENTIALS)
  @request_pool ||= create_request_pool(metadata_uri)
  request = Gem::Request.new(metadata_uri, Net::HTTP::Get, nil, @request_pool)
  response = request.fetch

  case response
  when Net::HTTPOK then
    JSON.parse(response.body)
  else
    raise InstanceProfileError.new("Unable to fetch AWS credentials from #{metadata_uri}: #{response.message} #{response.code}")
  end
end
fetch_s3_config() click to toggle source

Extracts S3 configuration for S3 bucket

# File lib/rubygems/s3_uri_signer.rb, line 110
def fetch_s3_config
  return S3Config.new(uri.user, uri.password, nil, "us-east-1") if uri.user && uri.password

  s3_source = Gem.configuration[:s3_source] || Gem.configuration["s3_source"]
  host = uri.host
  raise ConfigurationError.new("no s3_source key exists in .gemrc") unless s3_source

  auth = s3_source[host] || s3_source[host.to_sym]
  raise ConfigurationError.new("no key for host #{host} in s3_source in .gemrc") unless auth

  provider = auth[:provider] || auth["provider"]
  case provider
  when "env"
    id = ENV["AWS_ACCESS_KEY_ID"]
    secret = ENV["AWS_SECRET_ACCESS_KEY"]
    security_token = ENV["AWS_SESSION_TOKEN"]
  when "instance_profile"
    credentials = ec2_metadata_credentials_json
    id = credentials["AccessKeyId"]
    secret = credentials["SecretAccessKey"]
    security_token = credentials["Token"]
  else
    id = auth[:id] || auth["id"]
    secret = auth[:secret] || auth["secret"]
    security_token = auth[:security_token] || auth["security_token"]
  end

  raise ConfigurationError.new("s3_source for #{host} missing id or secret") unless id && secret

  region = auth[:region] || auth["region"] || "us-east-1"
  S3Config.new(id, secret, security_token, region)
end
generate_canonical_query_params(s3_config, date_time, credential_info, expiration) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 64
def generate_canonical_query_params(s3_config, date_time, credential_info, expiration)
  canonical_params = {}
  canonical_params["X-Amz-Algorithm"] = "AWS4-HMAC-SHA256"
  canonical_params["X-Amz-Credential"] = "#{s3_config.access_key_id}/#{credential_info}"
  canonical_params["X-Amz-Date"] = date_time
  canonical_params["X-Amz-Expires"] = expiration.to_s
  canonical_params["X-Amz-SignedHeaders"] = "host"
  canonical_params["X-Amz-Security-Token"] = s3_config.security_token if s3_config.security_token

  # Sorting is required to generate proper signature
  canonical_params.sort.to_h.map do |key, value|
    "#{base64_uri_escape(key)}=#{base64_uri_escape(value)}"
  end.join("&")
end
generate_canonical_request(canonical_host, query_params) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 79
def generate_canonical_request(canonical_host, query_params)
  [
    "GET",
    uri.path,
    query_params,
    "host:#{canonical_host}",
    "", # empty params
    "host",
    "UNSIGNED-PAYLOAD",
  ].join("\n")
end
generate_signature(s3_config, date, string_to_sign) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 100
def generate_signature(s3_config, date, string_to_sign)
  date_key = OpenSSL::HMAC.digest("sha256", "AWS4" + s3_config.secret_access_key, date)
  date_region_key = OpenSSL::HMAC.digest("sha256", date_key, s3_config.region)
  date_region_service_key = OpenSSL::HMAC.digest("sha256", date_region_key, "s3")
  signing_key = OpenSSL::HMAC.digest("sha256", date_region_service_key, "aws4_request")
  OpenSSL::HMAC.hexdigest("sha256", signing_key, string_to_sign)
end
generate_string_to_sign(date_time, credential_info, canonical_request) click to toggle source
# File lib/rubygems/s3_uri_signer.rb, line 91
def generate_string_to_sign(date_time, credential_info, canonical_request)
  [
    "AWS4-HMAC-SHA256",
    date_time,
    credential_info,
    Digest::SHA256.hexdigest(canonical_request)
  ].join("\n")
end