John Pliam > Apache-SecSess-0.09 > Apache::SecSess

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NAME ^

Apache::SecSess - Secure Apache session management library

SYNOPSIS ^

  In startup.pl,

    $My::obj = Apache::SecSess::Cookie::X509->new(...)

  In httpd.conf,

    <Location /protected>
      PerlAuthenHandler $My::obj->authen
      ...
    </Location>

  See section EXAMPLE below for more details.

DESCRIPTION ^

This package is a software library for managing HTTP and HTTPS session security within the Apache mod_perl framework. It offers the flexibility to securely configure distributed web services, across multiple hosts and domains, consistent with a common security policy.

In a complex environment, there could be several Perl objects whose methods are specific Apache phase handlers designed to manage a user's session lifecycle, including: initiating, renewing and terminating the session. Each of these objects is an instance of some subclass of Apache::SecSess, which treats a particular security paradigm.

CLASS HIERARCHY ^

Below is a diagram of the class hierarchy

  SecSess
   `+-Cookie
    | `+--BasicAuth (for debugging)
    |  +--LoginForm
    |  +--X509
    |  +--X509PIN
    |  `--URL
    `-URL
      `---Cookie

SecSess contains (in addition to common code) all Apache phase handlers (Currently only PerlAuthenHandler are needed). At this level credentials and status are considered opaque objects. The important methods are:

->authen() Used to protect underlying resources. Checks credentials for freshness and validity.

->issue() Used as the "initial" identity authentication before issuing credentials (cookies or mangled URLs) used by ->authen().

->renew() Will re-issue credentials if proper conditions are satisfied

->delete() Will delete credentials where relevant (i.e. deletes cookies).

At one level beneath SecSess (SecSess::Cookie.pm and SecSess::URL.pm), are the methods for interpreting and manipulating credentials.

At the lowest level, are subclasses which "know" how to interpret the *initial* identifying information during the issuance of credentials. So, *::Cookie::LoginForm presents the client with a user/password login form for identification. And thus the difference between *::Cookie::URL and *::URL::Cookie is that the former will issue cookies after validating an URL credential, and the latter will "issue" an URL credential (typically it will redirect to a resource with realm=cred in the URL) after validating a cookie.

CREDENTIAL FORMAT ^

Credentials in Apache::SecSess have a similar format:

    URL Credentials (defined in Apache::SecSess::URL):
        realm=E_k(md5(hash),hash)

    Cookie Credentials: (defined in Apache::SecSess::Cookie):
        realm:qop,authqop=E_k(md5(hash),hash)

The string 'realm' is any symbol (without obvious special characters ':', '=', etc) which is used to identify cooperating security services, thus providing a way to put credentials into their own namespace. The 'hash' is a string representation of a Perl hash of the form:

    hash = {uid => str, timestamp => int, qop => int, authqop => int}

See README and Wrapper.pm for further details.

ARGUMENTS ^

Credential Arguments

  authRealm => <realm>

Defines string 'realm' as identifying tag for credentials as described above in CREDENTIAL FORMAT.

  secretFile => <filename>

The first line of this file is used to create the secret encryption key for credentials as described above in CREDENTIAL FORMAT. This secret key is never given to users and should never leave the system servers.

Timing Arguments

  lifeTime => <minutes>

Session will expire after the specified number of minutes.

  idleTime => <minutes> 

A session idle for the specified number of minutes will time out.

  renewRate => <minutes>

A session which is constantly active will have a transparent renewal (resetting an implicit 'idle timer') every period of the specified number of minutes.

Quality of Protection Arguments

minSessQOP => 128, minAuthQOP => 128, authQOP => 128, sessQOP => 128

When credentials are validated during a request, two checks of the qualities of protection (QOP's) are made, namely that

        qop >= minSessQOP
and 
        authqop >= minAuthQOP

where qop and authqop indicate the session and user authentication protection or strength roughly measured in bits. They are the signed values appearing *inside* the credential hash described above. In the case of cookies, where multiple credentials with different security levels are may be present at request time, only the strongest credentials are used to make this determination. (The cleartext pairs (qop,authqop) are sorted lexicographically to determine which cookies to use. The cleartext values are not trusted.)

The QOP parameters are separated to allow flexibility in the threat model. In the simplest paradigm (and first demo examples), qop=0 and authqop=40, which merely indicates that the user ID's and passwords are protected with SSL but the web docs acquired with them are not. This is somewhat common over intranets. Under the stronger threat model of an active adversary who controls the untrusted network, true end-to-end security is required, but we may still wish to separate session and authentication qualities of protection. For example, if all SSL sessions never drop below 128-bits, we may still choose to allow weaker strength during user authentication, say with a 20-bit PIN or one-time password. Scientific cryptography cannot always afford to distinguish between an attack which costs 2^20 computations and one which succeeds with probability 1/2^20, because with 1 million users, the two situations are identical. But, for practical risk assessment, it may be perfectly acceptable to trade strong session credentials for weak login credentials.

The values of qop and authqop issued are determined by the Apache::SecSess object in all cases. For URL credentials they come directly from arguments sessQOP and authQOP, respectively. For cookie credentials, they come from the hash keys of the argument cookieDomain described below.

Note that no attempt is made to check the correctness of the QOP settings against the values of the httpd.conf directive SSLCipherSuite. This would be mistake in fact because the session strength is dependent on global factors as described in README. Nevertheless, you should check your assumptions about your local site's openssl with the script utils/minstren which prints the weakest cipher strength for common SSLCipherSuite arguments. At my site, I was surprised to find ALL:!ADH:!EXP:!EXP56 => 56 bits.

Cookie Domain Argument

  cookieDomain => <hashref>

The cookieDomain argument expects a hash reference of the form:

        { 'qop,authqop' => 'domain_string', ...  }

where 'domain_string' is literally the HTTP Set-Cookie domain string, and where the integers 'qop' and 'authqop' serve to define the session and authentication qualities of protections as described above. A cookie will be issued with the given domain and of the given strengths for each entry in this hash. The HTTP Set-Cookie secure flag is set if and only if 'qop' is nonzero. As a convenient shorthand,

        int => 'domain_string'

is equivalent to

        'int,int' => 'domain_string'

Here are some examples taken from the demo.

      cookieDomain => {0 => '.acme.com', 40 => '.acme.com'}

will set two cookies for the .acme.com domain: a non-secure one of form 'realm:0,0=value', and a secure one of form 'realm:40,40=value'.

      cookieDomain => {'0,40' => 'lysander.acme.com'}

will set a single non-secure cookie for the given host. This is a common paradigm for protecting passwords over an intranet.

      cookieDomain => {
        0 => '.acme.com',
        40 => '.acme.com',           # weak wildcard domain
        '64,128' => '.sec.acme.com', # stronger wildcard domain
        128 => 'milt.sec.acme.com'
      }

will set 4 cookies, all but the first being secure. In addition to an explicit hostname at the end, this declaration defines two wildcard domains, *.acme.com supporting any export crippled, SSLv2 host, and *.sec.acme.com which intended to have a minimum of 64 bits throughout.

Session State URL Arguments

These have the obvious meaning and must agree in host, scheme, and path with the corresponding Apache directives, as shown in the EXAMPLE section. Generally for example,

authenURL => Where to go to get the appropriate credentials for a requested resource.

defaultURL => Where to go after logging in (if no initial request was made).

timeoutURL => Where to go to delete credentials. Timeouts and signouts are both sent here.

URL Chaining Arguments

  chainURLS => <arrayref>, issueURL => <string>

Apache::SecSess is designed to use cookies for most local authentication. By their definition, cookies are restricted to a host, a DNS domain or subdomain. The subclass Apache::SecSess::URL, which allows you to span authentication across DNS domains, requires additional arguments to accomplish this. The argument chainURLS expects an array reference which defines a list of places to go for more (typically cookie) credentials. For example,

      chainURLS => [
        'https://milt.sec.acme.com/authen', 
        'https://noam.acme.org/authen'
      ]

says that when URL credentials are issued, the client will be redirected to each of the specified sites, in turn. Each of these is expected to be protected by a PerlAuthenHandler of type Apache::SecSess::Cookie::URL, which will issue local cookies.

The argument issueURL is used to tell the remote sites (listed in chainURLS arg) where to redirect the client back to, in order to continue chaining.

See the URL-Chaining example and the demo for more details.

Database Object Argument

 dbo => Apache::SecSess::DBI->new(
   dbifile => '/usr/local/apache/conf/private/dbilogin.txt'
 ),

UNFINISHED. Apache::SecSess was designed to abstractly handle user information. All user ID, password, X.509 DN queries are handled through an opaque object of class Apache::SecSess::DBI.

Since there is no documentation for this version, you must follow the instructions in INSTALL to get it to work. Read db/* for more info.

EXAMPLES ^

A Simple Cookie Example

Assuming all resources under directory /protected on one or more hosts in a DNS domain need to be protected, place the following directive into 'httpd.conf':

  <Location /protected>
    SetHandler perl-script
    PerlHandler Apache::YourContentHandler
    PerlAuthenHandler $Acme::obj->authen
    require valid-user
  </Location>

On each such host, the secure session object $Acme::obj must be instantiated from a 'startup.pl' file as in the following example, which uses an X.509 certificate for the original identification and authentication:

  use Apache::SecSess::DBI;
  use Apache::SecSess::Cookie::X509;

  ## X.509 certificate authentication, issuing multiple cookies
  $Acme::obj = Apache::SecSess::Cookie::X509->new(
      dbo => SecSessDBI->new( ... ),
      secretFile => 'ckysec.txt',
      lifeTime => 1440, idleTime => 60, renewRate => 5,
      authRealm => 'Acme',
      cookieDomain => {
          0 => '.acme.com',
          40 => '.acme.com',
          128 => 'tom.acme.com'
      },
      minSessQOP => 128, minAuthQOP => 128, 
      authenURL => 'https://tom.acme.com/authen',
      defaultURL => 'https://tom.acme.com/protected',
      renewURL => 'https://tom.acme.com/renew',
      timeoutURL => 'https://tom.acme.com/signout/timeout.html',
      errorURL => 'http://tom.acme.com/error.html'
  );

Now, on the host which issues credentials, (tom.acme.com in this example), add the following additional Apache directives to http.conf:

  ## issues cookies
  <Location /authen>
    SetHandler perl-script
    AuthName "Adam Realm"
    AuthType Basic
    PerlAuthenHandler $Acme::obj->issue
    require valid-user
  </Location>

  ## renew's cookies
  <Location /renew>
    SetHandler perl-script
    AuthName "Doesn't Matter"
    AuthType secsess
    PerlAuthenHandler $Acme::obj->renew
    require valid-user
  </Location>

  ## deletes cookies  
  <Location /signout>
    SetHandler perl-script
    AuthName "Doesn't Matter"
    AuthType secsess
    PerlAuthenHandler $Acme::obj->delete
    require valid-user
  </Location>

A URL-Chaining Example

In this example, a request for a resource in one DNS domain forces a login to a site on another DNS domain which repeatedly redirects the client to a list other sites for cookies. After all the chaining is finished, the client will be redirected back to the original request.

Suppose the original request is https://noam.acme.org/protected, which is handled by:

  <Location /protected>
      PerlAuthenHandler $Acme::noam->authen
      ...
  </Location>

where the authen() method is of an object of class Apache::SecSess::Cookie::URL instantiated as:

  $Acme::noam = Apache::SecSess::Cookie::URL->new(
    dbo => Apache::SecSess::DBI->new(...),
    secretFile => 'ckysec.txt',
    lifeTime => 1440, idleTime => 60, renewRate => 5,
    minSessQOP => 128, minAuthQOP => 128,
    authRealm => 'Acme',
    cookieDomain => { 128 => 'noam.acme.org' },
    authenURL => 'https://stu.transacme.com/chain',
    defaultURL => 'https://noam.acme.org/protected',
    renewURL => 'https://noam.acme.org/renew',
    timeoutURL => 'https://noam.acme.org/signout/timeout.html'
  );

Like any other subclass of Apache::SecSess::Cookie, URL.pm will issue cookies based on the presentation of some identifying information, and authenURL defines where to go to get that information. The difference is that it now points to a new DNS domain: stu.transacme.com.

That 'remote login' is protected by

  <Location /chain>
    PerlAuthenHandler $Acme::chain->issue
        ...
  </Location> 

i.e., the issue() method of the object $Acme::chain which is instantiated as

  $Acme::chain = Apache::SecSess::URL::Cookie->new(
    dbo => Apache::SecSess::DBI->new(...),
    secretFile => 'ckysec.txt',
    lifeTime => 1440, idleTime => 60, renewRate => 5,
    sessQOP => 128, authQOP => 128,
    minSessQOP => 128, minAuthQOP => 128,
    authRealm => 'Acme',
    authenURL => 'https://stu.transacme.com/authen',
    chainURLS => [
      'https://milt.sec.acme.com/authen', 
      'https://noam.acme.org/authen'
    ],
    issueURL => 'https://stu.transacme.com/chain',
    defaultURL => 'https://stu.transacme.com/protected',
    renewURL => 'https://stu.transacme.com/renew',
    timeoutURL => 'https://stu.transacme.com/signout/timeout.html'
  );

If no cookies are present, the client will be redirected again to https://stu.transacme.com/authen or the issue() method of a standard Cookie-based login:

  <Location /authen>
    PerlAuthenHandler $Acme::stu->issue
    ...
  </Location>

where $Acme::stu is an instance of, say Apache::SecSess::Cookie::X509, just as in the previous example.

But if and when cookies are present, $Acme::chain->issue will walk through the URL's listed in the chainURLS argument eventually getting to https://noam.acme.org/authen protected by

  <Location /authen>
    PerlAuthenHandler $Acme::noam->issue
    ...
  </Location>

which is the cookie issuing URL and issue() method, corresponding to the original request.

When all the URL-chaining is done, the issue() method of $Acme::chain, will automatically redirect back to https://noam.acme.org/protected.

SEE ALSO ^

See the README in the original distribution for further security architecture and motivation.

See RFC2109 and RFC2965, which describe the HTTP cookie protocol, and RFC2964 (BCP44) which presents some important caveats.

See demo/httpdconf/startup.pl and corresponding .conf files for complete working examples.

AUTHORS ^

John Pliam (pliam@atbash.com) coding and crypto protocols.

Jim Krajewski (jimk@echosoft.com) tips and techniques too numerous to mention.

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