FACTOTUM(2) FACTOTUM(2)
NAME
Factotum: attrtext, challenge, copyattrs, delattr, findattr,
findattrval, getuserpassd, mount, open, parseattrs, proxy,
publicattrs, takeattrs, respond, response, rpc, rpcattrs -
client interface to factotum
SYNOPSIS
include "factotum.m";
auth := load Factotum Factotum->PATH;
Authinfo: adt{
cuid: string; # ID on caller
suid: string; # ID on server
cap: string; # capability (only valid on server side)
secret: array of byte; # key for encryption
};
AuthRpcMax: con ...;
init: fn();
mount: fn(fd: ref Sys->FD, mnt: string, flags: int,
aname: string, keyspec: string): (int, ref Authinfo);
getuserpasswd: fn(keyspec: string): (string, string);
Challenge: adt {
user: string; # user (some protocols)
chal: string; # challenge string
};
challenge: fn(keyspec: string): ref Challenge;
response: fn(c: ref Challenge, resp: string): ref Authinfo;
respond: fn(chal: string, keyspec: string): (string, string);
open: fn(): ref Sys->FD;
rpc: fn(facfd: ref Sys->FD, verb: string, a: array of byte):
(string, array of byte);
proxy: fn(afd: ref Sys->FD, facfd: ref Sys->FD, arg: string):
ref Authinfo;
rpcattrs: fn(facfd: ref Sys->FD): list of ref Attr;
Attr: adt {
tag: int; # Aattr, Aval, or Aquery
name: string;
val: string;
text: fn(a: self ref Attr): string;
};
parseattrs: fn(s: string): list of ref Attr;
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copyattrs: fn(l: list of ref Attr): list of ref Attr;
delattr: fn(l: list of ref Attr, n: string): list of ref Attr;
takeattrs: fn(l: list of ref Attr, names: list of string): list of ref Attr;
findattr: fn(l: list of ref Attr, n: string): ref Attr;
findattrval: fn(l: list of ref Attr, n: string): string;
publicattrs: fn(l: list of ref Attr): list of ref Attr;
attrtext: fn(l: list of ref Attr): string;
DESCRIPTION
Factotum interacts with an instance of the authentication
agent factotum(4) to authenticate a client to a server. It
can also interact with Plan 9's factotum if that is in the
name space (as well as or instead of factotum(4)).
Factotum supports both the basic RPC interface to factotum
and various high-level operations built on that. The high-
level functions will be described first.
Init must be called before any other function.
Mount is similar to Sys->mount (see sys-bind(2)), but uses
factotum to authenticate, if the server requires it.
Factotum->mount should be used instead of Sys->mount when
mounting file servers that use attach(5) to authenticate.
(If the server on fd does not require authentication,
Factotum->mount simply calls Sys->mount.) Mount returns
(v,ai). If the integer v is non-negative, the mount suc-
ceeded; on error, v is negative, either the authentication
or the mount failed, ai is nil, and the system error string
contains a diagnostic. If the server required authentica-
tion and that was successful, ai is a non-nil reference to
an Authinfo value containing the agreed user IDs, a capabil-
ity for cap(3) that is valid only on the server, and an
array of bytes containing a shared secret that can be used
by client and server to create encryption and hashing keys
for the conversation.
Getuserpasswd returns a tuple (user,password) containing the
values for the user and !password attributes of a factotum
entry that has proto=pass and matches the given keyspec. The
tuple values are nil if no entry matches or the caller lacks
permission to see them.
The pair of functions challenge and response give servers
access to challenge/response protocols provided by factotum.
All such authentication protocols are embedded in an
application-level protocol such as FTP, IMAP, POP3 and so
on, in a way specific to that protocol. These functions
calculate parameters for application-specific messages.
A server calls challenge to get a challenge value to present
to the user who will answer the challenge. The server
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verifies the user's response by calling response, which
returns an Authinfo value (as described above) if the
response is correct. The specific challenge/response proto-
col is selected by the proto attribute in the keyspec for
challenge, which opens a connection to factotum, obtains a
string representing a challenge value, and returns a refer-
ence to a Challenge adt that gives the challenge and a user
name. Some protocols take the user name from a user
attribute in the keyspec, and others negotiate it within the
authentication protocol. In the latter case, the user field
of the resulting Challenge gives the name negotiated.
In the other direction, a process uses respond to calculate
the correct response to a given challenge. Chal is the
challenge presented by a server, and keyspec gives the
attributes of the relevant key in the local factotum.
Respond interacts with factotum and returns a tuple
(response, user) that gives the response string to return to
the server, and an optional user name, depending on the pro-
tocol. On error, the response is nil, and the system error
string contains a diagnostic.
Factotum(4) represents keys as attribute value pairs in tex-
tual form, with space-separated fields. A field can be a
value-less attribute, an attribute=value pair, or attribute?
to mark a required attribute with unknown value. An
attribute name that begins with an exclamation mark (!) is
to be considered hidden or secret. Values containing white
space or special characters can be quoted using the conven-
tions of sh(1).
Parseattrs parses a string s of that form into a list of
Attr references. Each Attr has a tag that identifies the
value as Aattr (a value-less attribute), a Aval (an
attribute-value pair), or Aquery (an attribute for which a
value is needed). Other operations include:
copyattrs Return a copy of attribute list l.
delattr Return a copy of l removing all attributes
with name n.
takeattrs Return the subset of list l that contains
only the attributes listed in names.
findattr Return a reference to the first Attr in l
with the name n.
findattrval Return the value of the first attribute in l
with name n; return nil if the attribute is
not found or has no value.
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publicattrs Return a copy of l in which all secret
attributes have been removed.
attrtext Return the textual representation of
attribute list l, acceptable to parseattrs.
The low-level interfaces to factotum are as follows.
Proxy links an authenticating server on afd with the
factotum agent on facfd. Typically facfd is the result of
calling Factotum->open, which is equivalent to
sys->open("/mnt/factotum/rpc", Sys->ORDWR)
Afd is a file descriptor that represents a connection to the
service that requires authentication. It is typically the
result of sys-open(2), dial(2), or sys-fauth(2). Params
gives any parameters for factotum, as a string containing
space-separated attr=value pairs. Proxy ferries messages
between the server and factotum until the end of the
selected authentication protocol. If authentication failed,
proxy returns nil; otherwise on success it always returns a
non-nil reference to an Authinfo value with contents as
above, but if the protocol does not supply that authentica-
tion data, all the values are nil.
Rpcattrs returns the initial attributes provided in the
start request, and any others added later by the protocol.
Rpc does one message exchange with the factotum on facfd. It
writes a message containing the given verb and optional
binary parameter a, and returns (v,a) where v is the
response string from factotum and a is an optional binary
parameter for that response. Exceptionally, v is the string
"rpc failure" if communication fails or a message is gar-
bled, or "no key" if rpc cannot find a suitable key. See
factotum(4) for details of the protocol.
AuthRpcMax is an integer constant giving the maximum size of
a message in an rpc exchange.
SOURCE
/appl/lib/factotum.b
SEE ALSO
sys-bind(2), sys-fauth(2), factotum(4), attach(5)
DIAGNOSTICS
Functions that return nil references on error also set the
system error string.
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