This library implements the OpenID protocol (http://openid.net/).
OpenID is a protocol to share identities on the network. The protocol
itself uses simple basic HTTP, adding reliability using digitally signed
Steps, as seen from the consumer (or relying partner).
- Show login form, asking for
- Get HTML page from
openid_identifier and lookup
<link rel="openid.server" href="server">
- Associate to server
- Redirect browser (302) to server using mode
asking to validate the given OpenID.
- OpenID server redirects back, providing digitally signed
conformation of the claimed identity.
- Validate signature and redirect to the target location.
A consumer (an application that allows OpenID login) typically
uses this library through openid_user/3.
In addition, it must implement the hook http_openid:
to define accepted OpenID servers. Typically, this hook is used to
provide a white-list of acceptable servers. Note that accepting any
OpenID server is possible, but anyone on the internet can setup a dummy
OpenID server that simply grants and signs every request. Here is an
:- multifile http_openid:openid_hook/1.
http_openid:openid_hook(trusted(_, OpenIdServer)) :-
By default, information who is logged on is maintained with the
session using http_session_assert/1
with the term
openid(Identity). The hooks
login/logout/logged_in can be used to provide alternative administration
of logged-in users (e.g., based on client-IP, using cookies, etc.).
To create a server, you must do four things: bind the handlers
openid_server/2 and openid_grant/1
to HTTP locations, provide a user-page for registered users and define
grant(Request, Options) hook to verify your users. An
example server is provided in in
- Call hook on the OpenID management library. Defined hooks are:
- Consider OpenID logged in.
- Logout OpenID
- True if OpenID is logged in
- grant(+Request, +Options)
- Server: Reply positive on OpenID
- trusted(+OpenID, +Server)
- True if Server is a trusted OpenID server
- Called if the server provided AX attributes
- x_parameter(+Server, -Name, -Value)
- Called to find additional HTTP parameters to send with the OpenID verify
- Associate the current HTTP session with OpenID. If another
OpenID is already associated, this association is first
- Remove the association of the current session with any OpenID
- True if session is associated with OpenID.
- True if OpenID is a validated OpenID associated
with the current session. The scenario for which this predicate is
designed is to allow an HTTP handler that requires a valid login to use
the transparent code below.
openid_user(Request, OpenID, ),
If the user is not yet logged on a sequence of redirects will follow:
- Show a page for login (default: page /openid/login), predicate reply_openid_login/1)
- By default, the OpenID login page is a form that is
submitted to the
verify, which calls openid_verify/2.
- openid_verify/2 does the
- Find the OpenID claimed identity and server
- Associate to the OpenID server
- redirects to the OpenID server for validation
- The OpenID server will redirect here with the
authetication information. This is handled by openid_authenticate/4.
- (Local) URL of page to enter OpenID information. Default is
the handler for openid_login_page/1
- See also
produces errors if login is invalid or cancelled.
- Create the OpenID form. This exported as a separate DCG, allowing
applications to redefine /openid/login and reuse this part of the page. Options
- URL of action to call. Default is the handler calling
- Buttons is a list of
img structures where the
points to an OpenID 2.0 endpoint. These buttons are displayed below the
OpenID URL field. Clicking the button sets the URL field and submits the
href is relative, clicking it opens the
given location after adding’openid.return_to' and‘stay'.
true, show a checkbox that allows the user to stay
- Handle the initial login form presented to the user by the relying party
(consumer). This predicate discovers the OpenID server, associates
itself with this server and redirects the user's browser to the OpenID
server, providing the extra openid.X name-value pairs. Options
is, against the conventions, placed in front of the Request
to allow for smooth cooperation with
- Specifies where the OpenID provider should return to. Normally, that is
the current location.
- Specifies the
openid.trust_root attribute. Defaults to the
root of the current server (i.e.,
- Specifies the
openid.realm attribute. Default is the
- Request the exchange of additional attributes from the
identity provider. See http_ax_attributes/2
The OpenId server will redirect to the
- True if OpenIDLogin is the typed id for OpenID
|OpenIDLogin ||ID as typed by user (canonized) |
|OpenID ||ID as verified by server |
|Server ||URL of the OpenID server |
- Find the public URL for Request that we can make
available to our identity provider. This must be an absolute URL
where we can be contacted. Before trying a configured version through
http_public_url/2, we try
to see wether the login message contains a referer parameter or wether
the browser provided one.
- Find current location of the server.
- New code should use http_current_host/4
with the option
+ProblemCert, +AllCerts, +FirstCert, +Error)
- Accept all certificates. We do not care too much. Only the user cares
s/he is not entering her credentials with a spoofed side. As we
redirect, the browser will take care of this.
-Server:url, -OpenID:url, -ReturnTo:url)
- Succeeds if Request comes from the OpenID server
and confirms that User is a verified OpenID user. ReturnTo
provides the URL to return to.
After openid_verify/2 has
redirected the browser to the OpenID server, and the OpenID
server did its magic, it redirects the browser back to this address. The
work is fairly trivial. If
cancel, the OpenId server denied. If
the OpenId server replied positive, but we must verify what the server
told us by checking the HMAC-SHA signature.
This call fails silently if their is no
field in the request.
openid(cancel) if request was cancelled by the OpenId
openid(signature_mismatch) if the HMAC signature check
- Realise the OpenID server. The protocol demands a POST request here.
- Handle the reply from checkid_setup_server/3.
If the reply is
yes, check the authority (typically the password) and if
all looks good redirect the browser to ReturnTo, adding the OpenID
properties needed by the Relying Party to verify the login.
- Calls openid_associate/4
openid_associate(URL, Handle, Assoc, ).
-Handle, -Assoc, +Options)
+Handle, -Assoc, +Options)
- Associate with an open-id server. We first check for a still valid old
association. If there is none or it is expired, we esstablish one and
remember it. Options:
- One of
http://specs.openid.net/auth/2.0 (default) or
- To be done
- Should we store known associations permanently? Where?