Class: Aws::Sigv4::Signer

Inherits:
Object
  • Object
show all
Defined in:
gems/aws-sigv4/lib/aws-sigv4/signer.rb

Overview

Utility class for creating AWS signature version 4 signature. This class provides two methods for generating signatures:

  • #sign_request - Computes a signature of the given request, returning the hash of headers that should be applied to the request.

  • #presign_url - Computes a presigned request with an expiration. By default, the body of this request is not signed and the request expires in 15 minutes.

Configuration

To use the signer, you need to specify the service, region, and credentials. The service name is normally the endpoint prefix to an AWS service. For example:

ec2.us-west-1.amazonaws.com => ec2

The region is normally the second portion of the endpoint, following the service name.

ec2.us-west-1.amazonaws.com => us-west-1

It is important to have the correct service and region name, or the signature will be invalid.

Credentials

The signer requires credentials. You can configure the signer with static credentials:

signer = Aws::Sigv4::Signer.new(
  service: 's3',
  region: 'us-east-1',
  # static credentials
  access_key_id: 'akid',
  secret_access_key: 'secret'
)

You can also provide refreshing credentials via the :credentials_provider. If you are using the AWS SDK for Ruby, you can use any of the credential classes:

signer = Aws::Sigv4::Signer.new(
  service: 's3',
  region: 'us-east-1',
  credentials_provider: Aws::InstanceProfileCredentials.new
)

Other AWS SDK for Ruby classes that can be provided via :credentials_provider:

  • Aws::Credentials
  • Aws::SharedCredentials
  • Aws::InstanceProfileCredentials
  • Aws::AssumeRoleCredentials
  • Aws::ECSCredentials

A credential provider is any object that responds to #credentials returning another object that responds to #access_key_id, #secret_access_key, and #session_token.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(service: , region: , access_key_id: , secret_access_key: , session_token: nil, **options) ⇒ Signer #initialize(service: , region: , credentials: , **options) ⇒ Signer #initialize(service: , region: , credentials_provider: , **options) ⇒ Signer

Returns a new instance of Signer.

Overloads:

  • #initialize(service: , region: , access_key_id: , secret_access_key: , session_token: nil, **options) ⇒ Signer

    Parameters:

    • :service (String) —

      The service signing name, e.g. 's3'.

    • :region (String) —

      The region name, e.g. 'us-east-1'.

    • :access_key_id (String)
    • :secret_access_key (String)
    • :session_token (String) —

      (nil)

  • #initialize(service: , region: , credentials: , **options) ⇒ Signer

    Parameters:

    • :service (String) —

      The service signing name, e.g. 's3'.

    • :region (String) —

      The region name, e.g. 'us-east-1'.

    • :credentials (Credentials) —

      Any object that responds to the following methods:

      • #access_key_id => String
      • #secret_access_key => String
      • #session_token => String, nil
      • #set? => Boolean
  • #initialize(service: , region: , credentials_provider: , **options) ⇒ Signer

    Parameters:

    • :service (String) —

      The service signing name, e.g. 's3'.

    • :region (String) —

      The region name, e.g. 'us-east-1'.

    • :credentials_provider (#credentials) —

      An object that responds to #credentials, returning an object that responds to the following methods:

      • #access_key_id => String
      • #secret_access_key => String
      • #session_token => String, nil
      • #set? => Boolean

Parameters:

  • options (Hash) (defaults to: {}) —

    a customizable set of options

Options Hash (options):

  • :unsigned_headers (Array<String>) — default: [] —

    A list of headers that should not be signed. This is useful when a proxy modifies headers, such as 'User-Agent', invalidating a signature.

  • :uri_escape_path (Boolean) — default: true —

    When true, the request URI path is uri-escaped as part of computing the canonical request string. This is required for every service, except Amazon S3, as of late 2016.

  • :apply_checksum_header (Boolean) — default: true —

    When true, the computed content checksum is returned in the hash of signature headers. This is required for AWS Glacier, and optional for every other AWS service as of late 2016.



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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 121

def initialize(options = {})
  @service = extract_service(options)
  @region = extract_region(options)
  @credentials_provider = extract_credentials_provider(options)
  @unsigned_headers = Set.new((options.fetch(:unsigned_headers, [])).map(&:downcase))
  @unsigned_headers << 'authorization'
  @unsigned_headers << 'x-amzn-trace-id'
  @unsigned_headers << 'expect'
  [:uri_escape_path, :apply_checksum_header].each do |opt|
    instance_variable_set("@#{opt}", options.key?(opt) ? !!options[opt] : true)
  end

  if options[:signing_algorithm] == :sigv4a
    raise ArgumentError, 'You are attempting to sign a' \
' request with sigv4a which requires aws-crt and version 1.4.0.crt or later of the aws-sigv4 gem.'\
' Please install the gem or add it to your gemfile.'
  end
end

Instance Attribute Details

#apply_checksum_header ⇒ Boolean (readonly)

When true the x-amz-content-sha256 header will be signed and returned in the signature headers.

Returns:

  • (Boolean) —

    When true the x-amz-content-sha256 header will be signed and returned in the signature headers.



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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 163

def apply_checksum_header
  @apply_checksum_header
end

#credentials_provider ⇒ #credentials (readonly)

Returns an object that responds to #credentials, returning an object that responds to the following methods:

  • #access_key_id => String
  • #secret_access_key => String
  • #session_token => String, nil
  • #set? => Boolean

Returns:

  • (#credentials) —

    Returns an object that responds to #credentials, returning an object that responds to the following methods:

    • #access_key_id => String
    • #secret_access_key => String
    • #session_token => String, nil
    • #set? => Boolean


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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 155

def credentials_provider
  @credentials_provider
end

#region ⇒ String (readonly)

Returns:

  • (String) 


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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 144

def region
  @region
end

#service ⇒ String (readonly)

Returns:

  • (String) 


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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 141

def service
  @service
end

#unsigned_headers ⇒ Set<String> (readonly)

Returns a set of header names that should not be signed. All header names have been downcased.

Returns:

  • (Set<String>) —

    Returns a set of header names that should not be signed. All header names have been downcased.



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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 159

def unsigned_headers
  @unsigned_headers
end

Instance Method Details

#presign_url(options) ⇒ HTTPS::URI, HTTP::URI

Signs a URL with query authentication. Using query parameters to authenticate requests is useful when you want to express a request entirely in a URL. This method is also referred as presigning a URL.

See Authenticating Requests: Using Query Parameters (AWS Signature Version 4) for more information.

To generate a presigned URL, you must provide a HTTP URI and the http method.

url = signer.presign_url(
  http_method: 'GET',
  url: 'https://my-bucket.s3-us-east-1.amazonaws.com/key',
  expires_in: 60
)

By default, signatures are valid for 15 minutes. You can specify the number of seconds for the URL to expire in.

url = signer.presign_url(
  http_method: 'GET',
  url: 'https://my-bucket.s3-us-east-1.amazonaws.com/key',
  expires_in: 3600 # one hour
)

You can provide a hash of headers that you plan to send with the request. Every 'X-Amz-*' header you plan to send with the request must be provided, or the signature is invalid. Other headers are optional, but should be provided for security reasons.

url = signer.presign_url(
  http_method: 'PUT',
  url: 'https://my-bucket.s3-us-east-1.amazonaws.com/key',
  headers: {
    'X-Amz-Meta-Custom' => 'metadata'
  }
)

Parameters:

  • options (Hash) —

    a customizable set of options

Options Hash (options):

  • :http_method (required, String) —

    The HTTP request method, e.g. 'GET', 'HEAD', 'PUT', 'POST', 'PATCH', or 'DELETE'.

  • :url (required, String, HTTPS::URI, HTTP::URI) —

    The URI to sign.

  • :headers (Hash) — default: {} —

    Headers that should be signed and sent along with the request. All x-amz-* headers must be present during signing. Other headers are optional.

  • :expires_in (Integer<Seconds>) — default: 900 —

    How long the presigned URL should be valid for. Defaults to 15 minutes (900 seconds).

  • :body (optional, String, IO) —

    If the :body is set, then a SHA256 hexdigest will be computed of the body. If :body_digest is set, this option is ignored. If neither are set, then the :body_digest will be computed of the empty string.

  • :body_digest (optional, String) —

    The SHA256 hexdigest of the request body. If you wish to send the presigned request without signing the body, you can pass 'UNSIGNED-PAYLOAD' as the :body_digest in place of passing :body.

  • :time (Time) — default: Time.now —

    Time of the signature. You should only set this value for testing.

Returns:

  • (HTTPS::URI, HTTP::URI) 


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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 377

def presign_url(options)

  creds = fetch_credentials

  http_method = extract_http_method(options)
  url = extract_url(options)

  headers = downcase_headers(options[:headers])
  headers['host'] ||= host(url)

  datetime = headers['x-amz-date']
  datetime ||= (options[:time] || Time.now).utc.strftime("%Y%m%dT%H%M%SZ")
  date = datetime[0,8]

  content_sha256 = headers['x-amz-content-sha256']
  content_sha256 ||= options[:body_digest]
  content_sha256 ||= sha256_hexdigest(options[:body] || '')

  params = {}
  params['X-Amz-Algorithm'] = 'AWS4-HMAC-SHA256'
  params['X-Amz-Credential'] = credential(creds, date)
  params['X-Amz-Date'] = datetime
  params['X-Amz-Expires'] = extract_expires_in(options)
  params['X-Amz-Security-Token'] = creds.session_token if creds.session_token
  params['X-Amz-SignedHeaders'] = signed_headers(headers)

  params = params.map do |key, value|
    "#{uri_escape(key)}=#{uri_escape(value)}"
  end.join('&')

  if url.query
    url.query += '&' + params
  else
    url.query = params
  end

  creq = canonical_request(http_method, url, headers, content_sha256)
  sts = string_to_sign(datetime, creq)
  url.query += '&X-Amz-Signature=' + signature(creds.secret_access_key, date, sts)
  url
end

#sign_event(prior_signature, payload, encoder) ⇒ Object

Signs a event and returns signature headers and prior signature used for next event signing.

Headers of a sigv4 signed event message only contains 2 headers * ':chunk-signature' * computed signature of the event, binary string, 'bytes' type * ':date' * millisecond since epoch, 'timestamp' type

Payload of the sigv4 signed event message contains eventstream encoded message which is serialized based on input and protocol

To sign events

headers_0, signature_0 = signer.sign_event(
  prior_signature, # hex-encoded string
  payload_0, # binary string (eventstream encoded event 0)
  encoder, # Aws::EventStreamEncoder
)

headers_1, signature_1 = signer.sign_event(
  signature_0,
  payload_1, # binary string (eventstream encoded event 1)
  encoder
)

The initial prior_signature should be using the signature computed at initial request

Note:

Since ':chunk-signature' header value has bytes type, the signature value provided needs to be a binary string instead of a hex-encoded string (like original signature V4 algorithm). Thus, when returning signature value used for next event siging, the signature value (a binary string) used at ':chunk-signature' needs to converted to hex-encoded string using #unpack



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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 291

def sign_event(prior_signature, payload, encoder)
  creds = fetch_credentials
  time = Time.now
  headers = {}

  datetime = time.utc.strftime("%Y%m%dT%H%M%SZ")
  date = datetime[0,8]
  headers[':date'] = Aws::EventStream::HeaderValue.new(value: time.to_i * 1000, type: 'timestamp')

  sts = event_string_to_sign(datetime, headers, payload, prior_signature, encoder)
  sig = event_signature(creds.secret_access_key, date, sts)

  headers[':chunk-signature'] = Aws::EventStream::HeaderValue.new(value: sig, type: 'bytes')

  # Returning signed headers and signature value in hex-encoded string
  [headers, sig.unpack('H*').first]
end

#sign_request(request) ⇒ Signature

Computes a version 4 signature signature. Returns the resultant signature as a hash of headers to apply to your HTTP request. The given request is not modified.

signature = signer.sign_request(
  http_method: 'PUT',
  url: 'https://domain.com',
  headers: {
    'Abc' => 'xyz',
  },
  body: 'body' # String or IO object
)

# Apply the following hash of headers to your HTTP request
signature.headers['host']
signature.headers['x-amz-date']
signature.headers['x-amz-security-token']
signature.headers['x-amz-content-sha256']
signature.headers['authorization']

In addition to computing the signature headers, the canonicalized request, string to sign and content sha256 checksum are also available. These values are useful for debugging signature errors returned by AWS.

signature.canonical_request #=> "..."
signature.string_to_sign #=> "..."
signature.content_sha256 #=> "..."

Parameters:

  • request (Hash)

Options Hash (request):

  • :http_method (required, String) —

    One of 'GET', 'HEAD', 'PUT', 'POST', 'PATCH', or 'DELETE'

  • :url (required, String, URI::HTTPS, URI::HTTP) —

    The request URI. Must be a valid HTTP or HTTPS URI.

  • :headers (optional, Hash) — default: {} —

    A hash of headers to sign. If the 'X-Amz-Content-Sha256' header is set, the :body is optional and will not be read.

  • :body (optional, String, IO) — default: 'X-Amz-Content-Sha256'ody. A sha256 checksum is computed of the body unless the 'X-Amz-Content-Sha256' header is set. —

    '') The HTTP request body. A sha256 checksum is computed of the body unless the 'X-Amz-Content-Sha256' header is set.

Returns:



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# File 'gems/aws-sigv4/lib/aws-sigv4/signer.rb', line 212

def sign_request(request)

  creds = fetch_credentials

  http_method = extract_http_method(request)
  url = extract_url(request)
  headers = downcase_headers(request[:headers])

  datetime = headers['x-amz-date']
  datetime ||= Time.now.utc.strftime("%Y%m%dT%H%M%SZ")
  date = datetime[0,8]

  content_sha256 = headers['x-amz-content-sha256']
  content_sha256 ||= sha256_hexdigest(request[:body] || '')

  sigv4_headers = {}
  sigv4_headers['host'] = headers['host'] || host(url)
  sigv4_headers['x-amz-date'] = datetime
  sigv4_headers['x-amz-security-token'] = creds.session_token if creds.session_token
  sigv4_headers['x-amz-content-sha256'] ||= content_sha256 if @apply_checksum_header

  headers = headers.merge(sigv4_headers) # merge so we do not modify given headers hash

  # compute signature parts
  creq = canonical_request(http_method, url, headers, content_sha256)
  sts = string_to_sign(datetime, creq)
  sig = signature(creds.secret_access_key, date, sts)

  # apply signature
  sigv4_headers['authorization'] = [
    "AWS4-HMAC-SHA256 Credential=#{credential(creds, date)}",
    "SignedHeaders=#{signed_headers(headers)}",
    "Signature=#{sig}",
  ].join(', ')

  # Returning the signature components.
  Signature.new(
    headers: sigv4_headers,
    string_to_sign: sts,
    canonical_request: creq,
    content_sha256: content_sha256
  )
end