Module: EventMachine::Protocols::SASLauth

Defined in:
lib/em/protocols/saslauth.rb

Overview

Implements SASL authd. This is a very, very simple protocol that mimics the one used by saslauthd and pwcheck, two outboard daemons included in the standard SASL library distro. The only thing this is really suitable for is SASL PLAIN (user+password) authentication, but the SASL libs that are linked into standard servers (like imapd and sendmail) implement the other ones.

SASL-auth is intended for reasonably fast operation inside a single machine, so it has no transport-security (although there have been multi-machine extensions incorporating transport-layer encryption).

The standard saslauthd module generally runs privileged and does its work by referring to the system-account files.

This feature was added to EventMachine to enable the development of custom authentication/authorization engines for standard servers.

To use SASLauth, include it in a class that subclasses EM::Connection, and reimplement the validate method.

The typical way to incorporate this module into an authentication daemon would be to set it as the handler for a UNIX-domain socket. The code might look like this:

EM.start_unix_domain_server( "/var/run/saslauthd/mux", MyHandler )
File.chmod( 0777, "/var/run/saslauthd/mux")

The chmod is probably needed to ensure that unprivileged clients can access the UNIX-domain socket.

It's also a very good idea to drop superuser privileges (if any), after the UNIX-domain socket has been opened. – Implementation details: assume the client can send us pipelined requests, and that the client will close the connection.

The client sends us four values, each encoded as a two-byte length field in network order followed by the specified number of octets. The fields specify the username, password, service name (such as imap), and the “realm” name. We send back the barest minimum reply, a single field also encoded as a two-octet length in network order, followed by either “NO” or “OK” - simplicity itself.

We enforce a maximum field size just as a sanity check. We do NOT automatically time out the connection.

The code we use to parse out the values is ugly and probably slow. Improvements welcome.

Constant Summary

MaxFieldSize =
128*1024

Instance Method Summary collapse

Instance Method Details

#post_initObject



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# File 'lib/em/protocols/saslauth.rb', line 85

def post_init
  super
  @sasl_data = ""
  @sasl_values = []
end

#receive_data(data) ⇒ Object



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# File 'lib/em/protocols/saslauth.rb', line 91

def receive_data data
  @sasl_data << data
  while @sasl_data.length >= 2
    len = (@sasl_data[0,2].unpack("n")).first
    raise "SASL Max Field Length exceeded" if len > MaxFieldSize
    if @sasl_data.length >= (len + 2)
      @sasl_values << @sasl_data[2,len]
      @sasl_data.slice!(0...(2+len))
      if @sasl_values.length == 4
        send_data( validate(*@sasl_values) ? "\0\002OK" : "\0\002NO" )
        @sasl_values.clear
      end
    else
      break
    end
  end
end

#validate(username, psw, sysname, realm) ⇒ Object



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# File 'lib/em/protocols/saslauth.rb', line 109

def validate username, psw, sysname, realm
  p username
  p psw
  p sysname
  p realm
  true
end