WebAuth::Krb5

(WebAuth context for Kerberos calls)

SYNOPSIS

    use WebAuth qw(:const);
    use WebAuth::Krb5;

    my $wa = WebAuth->new;
    eval {
        my $krb5 = WebAuth::Krb5->new ($wa);
        $krb5->init_via_keytab ($path);
        print $krb5->get_principal (WA_KRB5_CANON_LOCAL);
    }
    if ($@) {
        # ... handle exception ...
    }

DESCRIPTION

This Perl context represents a WebAuth Kerberos context. This context is used to make all Kerberos-related calls and can also store a Kerberos identity and its corresponding ticket cache. A context is normally initiated with credentials from a username and password, a keytab, an existing ticket cache, or an exported credential.

CLASS METHODS

As with WebAuth module functions, failures are signaled by throwing WebAuth::Exception rather than by return status.

new (WEBAUTH)

Create a new WebAuth::Krb5 object attached to the WebAuth context WEBAUTH. This is a convenience wrapper around the WebAuth krb5_new() method.

INSTANCE METHODS

As with WebAuth module functions, failures are signaled by throwing WebAuth::Exception rather than by return status.

change_password (PASSWORD[, ARGS])

Change the password of the user represented by the Kerberos context to PASSWORD. The WebAuth::Krb5 object must already contain the credentials required to change a password (normally a kadmin/changepw credential created with krb5_init_via_password() or read from a context created that way using krb5_init_via_cred()).

By default, the kpasswd protocol is used to do the password change. This behavior can be modified using the optional ARGS argument which, if present, should be a reference to a hash with one or more of the following keys:

command

The command to send. Currently only used for the remctl password change protocol.

host

The host to which to send the password change. Currently only used for the remctl password change protocol.

identity

The Kerberos principal of the password change service to which this command will authenticate in order to send the change. The default depends on the protocol. Currently this is only used for the remctl password change protocol, which defaults to the normal principal used by remctl clients when sending commands. However, normally this will be a principal that disallows TGS-REQ authentications rather than the remctl default.

If this principal disallows TGS-REQ authentications, credentials for this principal must already be present in the WebAuth::Krb5 object before making this call since they cannot be retrieved from the KDC without additional authentication credentials.

port

The port on the password change host to contact. Currently only used for the remctl password change protocol.

protocol

The password change protocol to use. Currently supported values are kpasswd and remctl. kpasswd is the default and takes no further parameters, so in that case ARGS should normally be omitted. This key should normally always be set.

subcommand

The subcommand to send. Currently only used for the remctl password change protocol.

timeout

How long to wait, in integer seconds, for a reply before giving up. Currently only used for the remctl password change protocol.

An example of doing a password change via the remctl protocol, using kadmin/changepw as the service principal and taking the other options from global configuration, with a ten-second timeout:

    my $wa = WebAuth->new;
    my $krb5 = WebAuth::Krb5->new ($wa);
    $krb5->init_via_password ('user', 'password', 'kadmin/changepw');
    my $args = {
        protocol   => 'remctl',
        host       => $PASSWORD_CHANGE_SERVER,
        port       => $PASSWORD_CHANGE_PORT,
        identity   => 'kadmin/changepw',
        command    => $PASSWORD_CHANGE_COMMAND,
        subcommand => $PASSWORD_CHANGE_SUBCOMMAND,
        timeout    => 10,
    };
    $krb5->change_password ('new-password', $args);

For the remctl protocol, the server must expose a command and subcommand that takes a single argument, the new password, and changes the password of the authenticated user.

export_cred ([PRINC])

Exports either a Kerberos TGT or a Kerberos service ticket obtained using the credentials in the WebAuth::Krb5 context, have been initialized via one of the init_via_* methods or import_cred first. In a scalar context, returns the encoded Kerberos ticket (as binary data), suitable for passing to import_cred() or putting into a WebAuth token. In a list context, returns a two-element list consisting of the encoded Kerberos ticket and the expiration time of the ticket in seconds since epoch.

get_principal ([CANON])

Returns the principal associated with the Kerberos context, which should have been initialized via one of the init_via_* methods or import_cred first. CANON should be one of WA_KRB5_CANON_NONE (specifying no principal canonicalization), WA_KRB5_CANON_LOCAL (specifying that the principal should be converted to a local name if possible), or WA_KRB5_CANON_STRIP (specifying that any realm information should be stripped). These constants are provided by the WebAuth module.

If WA_KRB5_CANON_LOCAL is specified but krb5_aname_to_localname returns an error, the fully-qualified principal will be returned.

If CANON is not specified, WA_KRB5_CANON_NONE is the default behavior.

import_cred (CRED[, CACHE])

Imports the provided credential, created with export_cred, into the given Kerberos context. If the context is not already initialized, it will be initialized with the identity specified by the credential. CACHE specifies where to store the credential cache for this context and will be used only if the context is not already initialized. If CACHE is not specified and the context is not initialized, a memory cache will be used and destroyed when the context is destroyed.

init_via_cache ([CACHE])

Initializes a Kerberos context from an existing ticket cache. If CACHE is not specified, the default Kerberos ticket cache is used.

init_via_keytab (KEYTAB[, PRINC[, CACHE]])

Initializes a Kerberos context by using the keys in the provided KEYTAB to get a Kerberos TGT. If CACHE is not specified, a memory cache will be used and destroyed when the context is destroyed.

PRINC specifies the principal for which to get tickets. If it is not specified, the first principal found in KEYTAB will be used.

init_via_password (USER, PASS[, PRINC[, KEYTAB[, SPRINC[, CACHE]]]])

Initializes a Kerberos context using the specified username/password to obtain a Kerberos TGT. If KEYTAB is specified and PRINC is not given, the TGT will be verified using the normal krb5_verify_init_creds function. If CACHE is not specified, a memory cache will be used and destroyed when the context is destroyed.

If SPRINC is given, it specifies the principal in KEYTAB to use for the validation. If it is not specified, undef, or the empty string, the first principal found in KEYTAB will be used.

If PRINC is given and defined, obtain credentials for that principal rather than a TGT. This is normally used to get a context with a kadmin/changepw service ticket to use to change the user's password. If this is specified, the validity of the acquired credentials will not be verified.

If KEYTAB is not given, the validity of the returned tickets are not verified. This should only be used when obtaining kadmin/changepw service tickets to change a password. Skipping this validation step otherwise opens one up to KDC impersonation attacks.

Returns the server principal used to verify the TGT if KEYTAB is given and PRINC is not given. Otherwise, returns undef.

make_auth (PRINC[, DATA])

Construct a Kerberos authenticator for the specified principal and return the authenticator, suitable for passing to krb5_rd_req (possibly by way of the read_auth method). If DATA is provided, it will be encrypted with krb5_mk_priv in the session key of the authenticator.

In a scalar context, returns the authenticator as binary data. In a list context, when DATA is given, returns a two-element list consisting of the authenticator and the encrypted DATA.

read_auth (REQUEST, KEYTAB[, PRINC[, CANON[, EDATA]]])

Read a REQUEST created with make_auth and returns the client principal of the authenticator. KEYTAB is used to decode the request, and PRINC must be the principal for which the REQUEST was encoded. If PRINC is not provided, undef, or the empty string, the first principal found in KEYTAB will be used.

The returned client principal is canonicalized following the rule specified in CANON, following the same rules as in get_principal(). If CANON is not specified, WA_KRB5_CANON_NONE is the default behavior.

If EDATA is provided, it is decrypted with krb5_rd_priv, and the return value in a list context will be a two-element list containing the principal and the decrypted data.

CAVEATS

A WebAuth::Krb5 object will retain a reference to the WebAuth object that was used to create it and will prevent the WebAuth context from being freed until the WebAuth::Krb5 object can be freed. This ensures that objects don't disappear at inappropriate times, but it also means that no memory allocated in the WebAuth context, even if unrelated to the WebAuth::Krb5 object, will be freed until all objects created from it are freed. Creating and holding on to references to WebAuth::Krb5 objects for long periods may therefore result in unexpected memory usage.

AUTHOR

Russ Allbery <eagle@eyrie.org>

SEE ALSO

WebAuth(3)

This module is part of WebAuth. The current version is available from <http://webauth.stanford.edu/>.

Last spun 2015-02-17 from POD modified 2015-02-16