# frozen-string-literal: true
require 'openssl'
begin
OpenSSL::Cipher.new("aes-256-ctr")
rescue OpenSSL::Cipher::CipherError
# :nocov:
raise LoadError, "Roda sessions plugin requires the aes-256-ctr cipher"
# :nocov:
end
require 'base64'
require 'json'
require 'securerandom'
require 'zlib'
class Roda
module RodaPlugins
# The sessions plugin adds support for sessions using cookies. It is the recommended
# way to support sessions in Roda applications.
#
# The session cookies are encrypted with AES-256-CTR and then signed with HMAC-SHA-256.
# By default, session data is padded to reduce information leaked based on the session size.
#
# Sessions are serialized via JSON, so session information should only store data that
# allows roundtrips via JSON (String, Integer, Float, Array, Hash, true, false, and nil).
# In particular, note that Symbol does not round trip via JSON, so symbols should not be
# used in sessions when this plugin is used. This plugin sets the
# +:sessions_convert_symbols+ application option to +true+ if it hasn't been set yet,
# for better integration with plugins that can use either symbol or string session or
# flash keys. Unlike Rack::Session::Cookie, the session is stored as a plain ruby hash,
# and does not convert all keys to strings.
#
# All sessions are timestamped and session expiration is enabled by default, with sessions
# being valid for 30 days maximum and 7 days since last use by default. Session creation time is
# reset whenever the session is empty when serialized and also whenever +clear_session+
# is called while processing the request.
#
# Session secrets can be rotated. See options below.
#
# The sessions plugin can transparently upgrade sessions from Rack::Session::Cookie
# if the default Rack::Session::Cookie coder and HMAC are used, see options below.
# It is recommended to only enable transparent upgrades for a brief transition period,
# and remove support for them once old sessions have converted or timed out.
#
# If the final cookie is too large (>=4096 bytes), a Roda::RodaPlugins::Sessions::CookieTooLarge
# exception will be raised.
#
# = Required Options
#
# The session cookies this plugin uses are both encrypted and signed, so two separate
# secrets are used internally. However, for ease of use, these secrets are combined into
# a single +:secret+ option. The +:secret+ option must be a string of at least 64 bytes
# and should be randomly generated. The first 32 bytes are used as the secret for the
# cipher, any remaining bytes are used for the secret for the HMAC.
#
# = Other Options
#
# :cookie_options :: Any cookie options to set on the session cookie. By default, uses
# <tt>httponly: true, path: '/', same_site: :lax</tt> so that the cookie is not accessible
# to javascript, allowed for all paths, and will not be used for cross-site non-GET requests
# that. If the +:secure+ option is not present in the hash, then
# <tt>secure: true</tt> is also set if the request is made over HTTPS. If this option is
# given, it will be merged into the default cookie options.
# :gzip_over :: For session data over this many bytes, compress it with the deflate algorithm (default: nil,
# so never compress). Note that compression should not be enabled if you are storing data in
# the session derived from user input and also storing sensitive data in the session.
# :key :: The cookie name to use (default: <tt>'roda.session'</tt>)
# :max_seconds :: The maximum number of seconds to allow for total session lifetime, starting with when
# the session was originally created. Default is <tt>86400*30</tt> (30 days). Can be set to
# +nil+ to disable session lifetime checks.
# :max_idle_sessions :: The maximum number of seconds to allow since the session was last updated.
# Default is <tt>86400*7</tt> (7 days). Can be set to nil to disable session idleness
# checks.
# :old_secret :: The previous secret to use, allowing for secret rotation. Must be a string of at least 64
# bytes if given.
# :pad_size :: Pad session data (after possible compression, before encryption), to a multiple of this
# many bytes (default: 32). This can be between 2-4096 bytes, or +nil+ to disable padding.
# :parser :: The parser for the serialized session data (default: <tt>JSON.method(:parse)</tt>).
# :serializer :: The serializer for the session data (default +:to_json.to_proc+).
# :skip_within :: If the last update time for the session cookie is less than this number of seconds from the
# current time, and the session has not been modified, do not set a new session cookie
# (default: 3600).
# :upgrade_from_rack_session_cookie_key :: The cookie name to use for transparently upgrading from
# Rack::Session:Cookie (defaults to <tt>'rack.session'</tt>).
# :upgrade_from_rack_session_cookie_secret :: The secret for the HMAC-SHA1 signature when allowing
# transparent upgrades from Rack::Session::Cookie. Using this
# option is only recommended during a short transition period,
# and is not enabled by default as it lowers security.
# :upgrade_from_rack_session_cookie_options :: Options to pass when deleting the cookie used by
# Rack::Session::Cookie after converting it to use the session
# cookies used by this plugin.
#
# = Not a Rack Middleware
#
# Unlike some other approaches to sessions, the sessions plugin does not use
# a rack middleware, so session information is not available to other rack middleware,
# only to the application itself, with the session not being loaded from the cookie
# until the +session+ method is called.
#
# If you need rack middleware to access the session information, then
# <tt>require 'roda/session_middleware'</tt> and <tt>use RodaSessionMiddleware</tt>.
# <tt>RodaSessionMiddleware</tt> passes the options given to this plugin.
#
# = Session Cookie Cryptography/Format
#
# Session cookies created by this plugin use the following format:
#
# urlsafe_base64(version + IV + auth tag + encrypted session data + HMAC)
#
# where:
#
# version :: 1 byte, currently must be 0, other values reserved for future expansion.
# IV :: 16 bytes, initialization vector for AES-256-CTR cipher.
# encrypted session data :: >=12 bytes of data encrypted with AES-256-CTR cipher, see below.
# HMAC :: 32 bytes, HMAC-SHA-256 of all preceding data plus cookie key (so that a cookie value
# for a different key cannot be used even if the secret is the same).
#
# The encrypted session data uses the following format:
#
# bitmap + creation time + update time + padding + serialized data
#
# where:
#
# bitmap :: 2 bytes in little endian format, lower 12 bits storing number of padding
# bytes, 13th bit storing whether serialized data is compressed with deflate.
# Bits 14-16 reserved for future expansion.
# creation time :: 4 byte integer in unsigned little endian format, storing unix timestamp
# since session initially created.
# update time :: 4 byte integer in unsigned little endian format, storing unix timestamp
# since session last updated.
# padding :: >=0 padding bytes specified in bitmap, filled with random data, can be ignored.
# serialized data :: >=2 bytes of serialized data in JSON format. If the bitmap indicates
# deflate compression, this contains the deflate compressed data.
module Sessions
DEFAULT_COOKIE_OPTIONS = {:httponly=>true, :path=>'/'.freeze, :same_site=>:lax}.freeze
DEFAULT_OPTIONS = {:key => 'roda.session'.freeze, :max_seconds=>86400*30, :max_idle_seconds=>86400*7, :pad_size=>32, :gzip_over=>nil, :skip_within=>3600}.freeze
DEFLATE_BIT = 0x1000
PADDING_MASK = 0x0fff
SESSION_CREATED_AT = 'roda.session.created_at'.freeze
SESSION_UPDATED_AT = 'roda.session.updated_at'.freeze
SESSION_SERIALIZED = 'roda.session.serialized'.freeze
SESSION_DELETE_RACK_COOKIE = 'roda.session.delete_rack_session_cookie'.freeze
# Exception class used when creating a session cookie that would exceed the
# allowable cookie size limit.
class CookieTooLarge < RodaError
end
def self.load_dependencies(app, opts=OPTS)
app.plugin :_after_hook
end
# Split given secret into a cipher secret and an hmac secret.
def self.split_secret(name, secret)
raise RodaError, "sessions plugin :#{name} option must be a String" unless secret.is_a?(String)
raise RodaError, "invalid sessions plugin :#{name} option length: #{secret.bytesize}, must be >=64" unless secret.bytesize >= 64
hmac_secret = secret = secret.dup.force_encoding('BINARY')
cipher_secret = secret.slice!(0, 32)
[cipher_secret.freeze, hmac_secret.freeze]
end
# Configure the plugin, see Sessions for details on options.
def self.configure(app, opts=OPTS)
plugin_opts = opts
opts = (app.opts[:sessions] || DEFAULT_OPTIONS).merge(opts)
co = opts[:cookie_options] = DEFAULT_COOKIE_OPTIONS.merge(opts[:cookie_options] || OPTS).freeze
opts[:parser] ||= app.opts[:json_parser] || JSON.method(:parse)
opts[:serializer] ||= app.opts[:json_serializer] || :to_json.to_proc
if opts[:upgrade_from_rack_session_cookie_secret]
opts[:upgrade_from_rack_session_cookie_key] ||= 'rack.session'
rsco = opts[:upgrade_from_rack_session_cookie_options] = Hash[opts[:upgrade_from_rack_session_cookie_options] || OPTS]
rsco[:path] ||= co[:path]
rsco[:domain] ||= co[:domain]
end
opts[:cipher_secret], opts[:hmac_secret] = split_secret(:secret, opts[:secret])
opts[:old_cipher_secret], opts[:old_hmac_secret] = (split_secret(:old_secret, opts[:old_secret]) if opts[:old_secret])
case opts[:pad_size]
when nil
# no changes
when Integer
raise RodaError, "invalid :pad_size: #{opts[:pad_size]}, must be >=2, < 4096" unless opts[:pad_size] >= 2 && opts[:pad_size] < 4096
else
raise RodaError, "invalid :pad_size option: #{opts[:pad_size].inspect}, must be Integer or nil"
end
app.opts[:sessions] = opts.freeze
app.opts[:sessions_convert_symbols] = true unless app.opts.has_key?(:sessions_convert_symbols)
end
module InstanceMethods
# Clear data from the session, and update the request environment
# so that the session cookie will use a new creation timestamp
# instead of the previous creation timestamp.
def clear_session
session.clear
env.delete(SESSION_CREATED_AT)
env.delete(SESSION_UPDATED_AT)
nil
end
private
# If session information has been set in the request environment,
# update the rack response headers to set the session cookie in
# the response.
def _roda_after_50__sessions(res)
if res && (session = env['rack.session'])
@_request.persist_session(res[1], session)
end
end
end
module RequestMethods
# Load the session information from the cookie. With the sessions
# plugin, you must call this method to get the session, instead of
# trying to access the session directly through the request environment.
# For maximum compatibility with other software that uses rack sessions,
# this method stores the session in 'rack.session' in the request environment,
# but that does not happen until this method is called.
def session
@env['rack.session'] ||= _load_session
end
# Persist the session data as a cookie. If transparently upgrading from
# Rack::Session::Cookie, mark the related cookie for expiration so it isn't
# sent in the future.
def persist_session(headers, session)
opts = roda_class.opts[:sessions]
if session.empty?
if env[SESSION_SERIALIZED]
# If session was submitted and is now empty, remove the cookie
Rack::Utils.delete_cookie_header!(headers, opts[:key])
# else
# If no session was submitted, and the session is empty
# then there is no need to do anything
end
elsif cookie_value = _serialize_session(session)
cookie = Hash[opts[:cookie_options]]
cookie[:value] = cookie_value
cookie[:secure] = true if !cookie.has_key?(:secure) && ssl?
Rack::Utils.set_cookie_header!(headers, opts[:key], cookie)
end
if env[SESSION_DELETE_RACK_COOKIE]
Rack::Utils.delete_cookie_header!(headers, opts[:upgrade_from_rack_session_cookie_key], opts[:upgrade_from_rack_session_cookie_options])
end
nil
end
private
# Load the session by looking for the appropriate cookie, or falling
# back to the rack session cookie if configured.
def _load_session
opts = roda_class.opts[:sessions]
cs = cookies
if data = cs[opts[:key]]
_deserialize_session(data)
elsif (key = opts[:upgrade_from_rack_session_cookie_key]) && (data = cs[key])
_deserialize_rack_session(data)
end || {}
end
# If 'rack.errors' is set, write the error message to it.
# This is used for errors that shouldn't be raised as exceptions,
# such as improper session cookies.
def _session_serialization_error(msg)
return unless error_stream = @env['rack.errors']
error_stream.puts(msg)
nil
end
# Interpret given cookie data as a Rack::Session::Cookie
# serialized session using the default Rack::Session::Cookie
# hmac and coder.
def _deserialize_rack_session(data)
opts = roda_class.opts[:sessions]
key = opts[:upgrade_from_rack_session_cookie_key]
secret = opts[:upgrade_from_rack_session_cookie_secret]
data, digest = data.split("--", 2)
unless digest
return _session_serialization_error("Not decoding Rack::Session::Cookie session: invalid format")
end
unless Rack::Utils.secure_compare(digest, OpenSSL::HMAC.hexdigest(OpenSSL::Digest::SHA1.new, opts[:upgrade_from_rack_session_cookie_secret], data))
return _session_serialization_error("Not decoding Rack::Session::Cookie session: HMAC invalid")
end
begin
session = Marshal.load(data.unpack('m').first)
rescue
return _session_serialization_error("Error decoding Rack::Session::Cookie session: not base64 encoded marshal dump")
end
# Mark rack session cookie for deletion on success
env[SESSION_DELETE_RACK_COOKIE] = true
# Convert the rack session by roundtripping it through
# the parser and serializer, so that you would get the
# same result as you would if the session was handled
# by this plugin.
env[SESSION_SERIALIZED] = data = opts[:serializer].call(session)
env[SESSION_CREATED_AT] = Time.now.to_i
opts[:parser].call(data)
end
# Interpret given cookie data as a Rack::Session::Cookie
def _deserialize_session(data)
opts = roda_class.opts[:sessions]
begin
data = Base64.urlsafe_decode64(data)
rescue ArgumentError
return _session_serialization_error("Unable to decode session: invalid base64")
end
length = data.bytesize
if data.length < 61
# minimum length (1+16+12+32) (version+cipher_iv+minimum session+hmac)
# 1 : version
# 16 : cipher_iv
# 12 : minimum_session
# 2 : bitmap for gzip + padding info
# 4 : creation time
# 4 : update time
# 2 : data
# 32 : HMAC-SHA-256
return _session_serialization_error("Unable to decode session: data too short")
end
unless data.getbyte(0) == 0
# version marker
return _session_serialization_error("Unable to decode session: version marker unsupported")
end
encrypted_data = data.slice!(0, length-32)
unless Rack::Utils.secure_compare(data, OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, opts[:hmac_secret], encrypted_data+opts[:key]))
if opts[:old_hmac_secret] && Rack::Utils.secure_compare(data, OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, opts[:old_hmac_secret], encrypted_data+opts[:key]))
use_old_cipher_secret = true
else
return _session_serialization_error("Not decoding session: HMAC invalid")
end
end
encrypted_data.slice!(0)
cipher = OpenSSL::Cipher.new("aes-256-ctr")
# Not rescuing cipher errors. If there is an error in the decryption, that's
# either a bug in the plugin that needs to be fixed, or an attacker is already
# able to forge a valid HMAC, in which case the error should be raised to
# alert the application owner about the problem.
cipher.decrypt
cipher.key = opts[use_old_cipher_secret ? :old_cipher_secret : :cipher_secret]
cipher_iv = cipher.iv = encrypted_data.slice!(0, 16)
data = cipher.update(encrypted_data) << cipher.final
bitmap, created_at, updated_at = data.unpack('vVV')
padding_bytes = bitmap & PADDING_MASK
if (max = opts[:max_seconds]) && Time.now.to_i > created_at + max
return _session_serialization_error("Not returning session: maximum session time expired")
end
if (max = opts[:max_idle_seconds]) && Time.now.to_i > updated_at + max
return _session_serialization_error("Not returning session: maximum session idle time expired")
end
data = data.slice(10+padding_bytes, data.bytesize)
if bitmap & DEFLATE_BIT > 0
data = Zlib::Inflate.inflate(data)
end
env = @env
env[SESSION_CREATED_AT] = created_at
env[SESSION_UPDATED_AT] = updated_at
env[SESSION_SERIALIZED] = data
opts[:parser].call(data)
end
def _serialize_session(session)
opts = roda_class.opts[:sessions]
env = @env
now = Time.now.to_i
json_data = opts[:serializer].call(session).force_encoding('BINARY')
if (serialized_session = env[SESSION_SERIALIZED]) &&
(updated_at = env[SESSION_UPDATED_AT]) &&
(now - updated_at < opts[:skip_within]) &&
(serialized_session == json_data)
return
end
bitmap = 0
json_length = json_data.bytesize
gzip_over = opts[:gzip_over]
if gzip_over && json_length > gzip_over
json_data = Zlib.deflate(json_data)
json_length = json_data.bytesize
bitmap |= DEFLATE_BIT
end
# When calculating padding bytes to use, include 10 bytes for bitmap and
# session create/update times, so total size of encrypted data is a
# multiple of pad_size.
if (pad_size = opts[:pad_size]) && (padding_bytes = (json_length+10) % pad_size) != 0
padding_bytes = pad_size - padding_bytes
bitmap |= padding_bytes
padding_data = SecureRandom.random_bytes(padding_bytes)
end
session_create_time = env[SESSION_CREATED_AT]
serialized_data = [bitmap, session_create_time||now, now].pack('vVV')
serialized_data << padding_data if padding_data
serialized_data << json_data
cipher = OpenSSL::Cipher.new("aes-256-ctr")
cipher.encrypt
cipher.key = opts[:cipher_secret]
cipher_iv = cipher.random_iv
encrypted_data = cipher.update(serialized_data) << cipher.final
data = String.new
data << "\0" # version marker
data << cipher_iv
data << encrypted_data
data << OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, opts[:hmac_secret], data+opts[:key])
data = Base64.urlsafe_encode64(data)
if data.bytesize >= 4096
raise CookieTooLarge, "attempted to create cookie larger than 4096 bytes"
end
data
end
end
end
register_plugin(:sessions, Sessions)
end
end