Delegated dialogs allow one application to embed a creation or selection UI into another using HTML
iframe elements and JavaScript code. The embedded dialog notifies the parent page of resize or
submit events using HTML5 postMessage.
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OSLC specifications target specific integration scenarios. In some cases, allowing one application to delegate
to a user interface defined in another application is a more effective way to support a use case than an HTTP
interface that can only be accessed programmatically. There are two cases where this is especially true:
Resource creation: when a user of a web application needs to create a new resource in another
application. In this case, the web application asks the other server to provide a UI for resource creation,
and the server notifies the application when the creation has been completed or canceled by the user.
Resource selection: when a user of a web application needs to pick a resource managed by another
application. In this case, the web application asks the other server to provide a UI for resource selection,
and the server notifies the application when a resource or resources has been selected or if the selection was
canceled.
Delegated dialogs support these two cases. They allow one application to embed a creation or selection UI into
another using HTML iframe elements and JavaScript code.
Fig. 1Creation Dialog
Fig. 1Creation Dialog depicts what a defect creation dialog might look like inside a quality management
tool, displayed when the user clicks the Open Bug button. The dialog content itself comes from the change
management tool, running on another server. The dialog displays seamlessly inside the quality management
application, however, while retaining the change management tool's look and feel and capabilities.
Delegated dialogs provide a simple way for an end user to create or select resources from another application,
thus eliminating the need to rebuild the other application's dialog and its application logic.
1.1 Terminology
Terminology uses and extends the terminology and capabilities of
OSLC Core Overview, W3C Linked Data Platform [LDP], W3C's Architecture of
the World Wide Web [WEBARCH], and Hyper-text Transfer Protocol [HTTP11].
The following terms are used in discussions of dialogs:
Dialog
A web page for creating or selecting resources to be embedded inside another application.
Dialog Descriptor
A resource that describes information about a dialog such as its title and dimensions. In RDF
representations, the dialog descriptor has RDF type oslc:Dialog. See
5.Resource Constraints.
Prefill
A method of setting initial field values in a creation dialog.
1.3 Typographical Conventions and Use of RFC Terms
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples,
and notes in this specification are non-normative. Everything else in this specification is
normative.
The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY,
and OPTIONAL in this specification are to be interpreted as described in [RFC2119].
LDP containers [LDP] advertise their support for dialogs using the HTTP Link header
[RFC5988]. Each dialog type, creation or selection, has its own link relation.
Dialog Type
Link Relation
Creation
http://open-services.net/ns/core#creationDialog
Selection
http://open-services.net/ns/core#selectionDialog
The client discovers the dialogs by making an HTTP OPTIONS request on the container.
Example 1: An OPTIONS Request on the Container
OPTIONS /bugs/ HTTP/1.1
Host: example.com
The server response contains a Link header with URLs to the dialog descriptors.
Clients can also use the HTTP Prefer header to find the dialogs for a container. The client makes
an HTTP GET request on the resource URI using the return=representation preference [RFC7240]
and include parameter [LDP] value http://open-services.net/ns/core#PreferDialog.
The server responds with the dialog descriptors in the response body. Clients should also use
include parameter value http://www.w3.org/ns/ldp#PreferMinimalContainer so that the
response doesn't include unnecessary data.
The following example shows a container that supports creation and selection dialogs:
2.3 Discovering Dialogs Using the Service resource
This section is non-normative.
Servers may also advertise their support for dialogs using the oslc:creationDialog and
oslc:selectionDialog properties of the Service discovery resource.
The client discovers the dialogs by making a GET request on the Service resource and accessing these
properties.
Example 7: An OPTIONS Request on the Container
GET /serviceproviders/bugs/services.xml HTTP/1.1
Host: example.com
Accept: application/rdf+xml
The server response contains a Service resource which contains properties with URLs to the dialog descriptors.
The client then requests the dialog to display using the discovered URI in the
oslc:dialog property in order to display the desired form.
Example 9
GET /dialogs/selectBug/form HTTP/1.1
Host: example.com
3. Using Dialogs
This section is non-normative.
Servers can offer two kinds of dialogs, selection dialogs and creation dialogs. Clients use selection dialogs
when they want a user to pick a resource from another application. They use creation dialogs when they want a
user to create a new resource in another application.
A client can open the dialog in a new browser window, or it can embed the dialog in another page by creating an
iframe element and setting the src attribute to the URI of the dialog to be included.
Example 10: Display a Dialog
var iframe =
document.createElement("iframe");
iframe.style.border =0;
iframe.style.width ="600px";// or preferred dialog width
iframe.style.height ="400px";// or preferred dialog height
iframe.src ="http://example.com/dialogs/createBug/form";
document.getElementById("dialogContainer").appendChild(iframe);
Clients might choose to place dialogs inside page elements styled to look like a dialog window.
Fig. 2Dialog iframe
The iframe itself, outlined in Fig. 2Dialog iframe, contains the dialog content from the
server.
Dialogs send results back to the client using the HTML5 function
Window.postMessage [webmessaging]. postMessage is called on
window.opener if set. Otherwise, postMessage is called on window.parent.
When embedded in an iframe, dialogs may also request to be resized dynamically. These requests are
the same as specified in OSLC Resource Preview and also use
postMessage. Clients can distinguish between results and resize messages from the message prefix.
Messages have the following prefixes:
Message Prefix
Meaning
oslc-response:
The user has created or selected resources or canceled the dialog.
oslc-resize:
The dialog is asking to be resized.
A stringified JSON object will be concatenated to the message prefix. For dialog responses, the JSON is
described by Appendix A.Dialog Results JSON. It is a JSON object with an oslc:results array of
results. Each result is a JSON object with an rdf:resource property whose value is the resource
URI. The result may also have an oslc:label that can be useful for client to display a label for
the delegated dialog.
Example 11: Dialog Results Message
oslc-response:{"oslc:results":
[{ "oslc:label": "bug 123: server crash", "rdf:resource": "http://example.com/bug123" }]}
An empty array indicates the dialog was canceled.
For resize requests, the JSON is an object with an oslc:hintHeight property, an
oslc:hintWidth property, or both.
Open the dialog in a new window using the Window.open() method or embed the dialog in an
iframe, setting iframesrc to the URI of the dialog.
Add a message listener to receive messages from the dialog.
Listen for message events, ignoring unrecognized events from other sources or those not
prefixed with oslc-response:
When message from the dialog indicates a completed action, free resources and handle the action.
Example 13: Listen for Dialog Results
window.addEventListener("message",function(event){// Make sure the message originated from the same origin as the dialog.if(event.origin !=="http://example.com"){return;}// Make sure the message starts with oslc-response:var message =event.data;if(message.indexOf("oslc-response:")!==0){return;}// Handle each result.var response = JSON.parse(message.substr("oslc-response:".length));var results = response["oslc:results"];for(var i =0; i < results.length; i++){var label = results[i]["oslc:label"];var uri = results[i]["rdf:resource"];// Handle resource...}// Remove the dialog from the page.var dialogContainer = document.getElementById('dialogContainer');
dialogContainer.removeChild(dialogContainer.firstChild);},false);
3.2 The Server's Responsibilities
This section is non-normative.
Provide the dialog, an HTML page for resource creation or selection.
Allow the user to perform resource creation or selection.
Once the user has created or selected a resource or canceled the dialog, send notification using
postMessage to the page's opener or parent window prefixed with "oslc-response:".
The following JavaScript code example shows how a dialog would send a response using postMessage,
taking into account pages that the dialog might be in its own window or an iframe.
Example 14
function respondWithSelection(label, uri){var response ={"oslc:results":[{"oslc:label": label,"rdf:resource": uri
}]};(window.opener || window.parent).postMessage("oslc-response:"+ JSON.stringify(response),"*");}
3.3 Prefill
This section is non-normative.
Servers may support setting the initial values in a dialog. A client can test if a dialog supports prefill by
making an HTTP OPTIONS request to the dialog descriptor URI. Prefill can be used with creation dialogs to
provide a template of initial values. Clients can use prefill with selection dialogs to inform servers about
the users desired content in the selection dialog.
The content of the request depends on the type of dialog and the server. Servers may describe constraints on
POST content using ResourceShapes. The dialog descriptor uses property
oslc:resourceShape for the shape constraints.
The server's response contains a Location header with the prefilled dialog's URI. The client uses
this as the iframe src.
Example 18: The Server Responds with the Dialog Location
HTTP/1.1 201 Created
Location: http://example.com/dialogs/createBug/form/2zFy45
The client then uses the dialog URI from the Location like any other dialog. The dialog URI from
a prefill request is often temporary. After a reasonable time, the server might respond with 404 Not Found or
410 Gone.
Clickjacking is a vulnerability that can occur when a
malicious (or compromised) web application embeds an OSLC delegated dialog in the application in such a way
that the user is tricked into using their authenticated session with the dialog, believing that they are
performing an operation other than the one indicated on the delegated dialog. The clickjacking application
embeds it own web page in a way that means the dialog is not clearly visible to the user, either almost
invisible, or hidden behind other components). When the user attempts to click on the visible components, the
browser interprets this as a click on the obscured delegated dialog, and the components within it. The
malicious web page encourages the user to click one of the visible components, which the user might believe
will not have side-effects (such as a link saying "If you are not redirected within 2 seconds, click here"),
but places that component over a component in the delegated dialog that the malicious page wishes the user to
click unknowingly. The user attempts to click on the visible component, but the browser interprets that as a
click on the hidden component, which will perform some action that the user is authorised to do (but the
malicious web page is not) but that the user did not intend to perform.
This vulnerability requires that the user loads a malicious web page in their browser. This can happen in a
number of ways, including:
The user is tricked into loading the page directly, believing it to be trustworthy.
A trusted page is compromised and "infected" to perform this attack.
An OSLC server administrator is tricked into configuring their server to trust a malicious server. Their
server then loads the malicious page as a delegated dialog or rich UI preview, which then embeds the page
under attack in a further iframe.
There are always two pages involved in this attack; the "UI consumer" page (which has the iframe embedded
within it), and the "UI provider" page (which gets loaded within the iframe). Consider the UI provider's
server the "server under attack".
To protect against this attack:
When requesting the URL for the delegated dialog (from the ServiceProvider) or the UI preview (from the
compact resource), the server under attack must require requests for the ServiceProvider to be
authenticated. This authentication must be for the end-user, not for the client app itself. That is, access
to the dialog URIs should be protected, as well as access to the dialogs themselves.
When returning a URL for the dialog or preview, the server under attack must return a URL that is specific
to the authenticated user, and that cannot be guessed by merely knowing the user's username or ID.
When the server under attack receives a request for the dialog or preview URL itself (the request that is
generated by the iframe to load the page to display within it), the server under attack must check that the
URL that was requested is one that was generated for the same user that is requesting this page (i.e. the
user that is identified by a session ID in the cookies sent with the request). This makes sure that the
client can't get a URL for the dialog from one user that it is authenticated for, and use that to perform a
clickjacking attack on another user that has not authorized that client.
If the users (for the URL and the cookie) do not match, then the server can either return with an HTTP
error, or include an
X-Frame-Options
header with value SAMEORIGIN or DENY.
This is only required on dialogs or resource previews that contain controls that can be invoked with one or
more clicks, and where those controls have side effects on the server. That is, if there are no controls on a
preview, then there is no target for the malicious page to tick the user to click on.
By following these steps the server under attack knows that only clients that are able to authenticate against
the server (e.g. for OAuth authentication they must have a valid client ID and - if required by the
interaction pattern they're using - they must know the client secret), and that have also been authorized by
the user to whom the the dialog is displayed, can display that dialog.
There are still some potential attack vectors:
The server administrator could authorize a malicious client app.
The user could authorize a malicious app to authenticate with the server under attack on their behalf.
But the exposure has been reduced as the attack cannot occur simply by loading a malicious web page in the
user's browser. See the OWASP
Clickjacking Defense Cheat Sheet
for further information.
4. Implementation Conformance
4.1 Discovery
In responses to successful HTTP requests for an LDP container that has a selection dialog, server MUST
include a Link header [RFC5988] where:
Servers MUST honor a client's request to inline dialog descriptors if the target resource has any dialog
descriptors and the request is successful.
[DD-4]
Servers MUST express the oslc:hintWidth and oslc:hintHeight properties of an
oslc:Dialog in length units as specified in [CSS21].
[DD-5]
In responses to HTTP GET requests targeting resources that have dialogs, servers SHOULD either include a
Vary response header with at least Accept and Prefer field values or a
Cache-Control header value no-store.
[DD-6]
Servers MAY also provide delegated dialog discovery using the
ServiceProvider and
Service resource and the oslc:creationDialog and
oslc:selectionDialog properties.
[DD-7]
4.2 Display
When embedding a dialog inside another web page, the client MUST use an iframe element and set
the its src attribute to the URI of the dialog.
[DD-8]
4.3 Messaging
Servers MUST support the Window.postMessage method [webmessaging] for dialog responses.
[DD-9]
Servers MAY support the
Window Name Protocol
defined in [OSLCCore2] for backward compatibility with OSLC 2.0 clients that use that protocol.
[DD-10]
Servers MAY support other protocols for dialog responses not specified in this document, which clients request
by appending a fragment identifier [RFC3986] describing the protocol to the end of the dialog URI.
[DD-11]
Servers MUST use postMessage for dialog responses if a client has not added a fragment identifier
to the dialog URI, or the fragment identifier is #oslc-core-postMessage-1.0.
[DD-12]
Messages describing dialog results MUST start with the characters
oslc-response: followed by JSON as specified in Appendix A.Dialog Results JSON.
[DD-13]
Example 22
oslc-response:{"oslc:results":
[{ "oslc:label": "bug 123: server crash", "rdf:resource": "http://example.com/bug123" }]}
Servers MAY include additional server-specific properties in the results JSON.
[DD-14]
If the user cancels a dialog, the dialog MUST still send a message with an empty
oslc:results array.
[DD-15]
Example 23
oslc-response:{"oslc:results": []}
Calls to postMessage from within a dialog MUST be made on window.opener unless
null or undefined.
[DD-16]
If window.opener is null or undefined, calls to
postMessageMUST be made on window.parent.
[DD-17]
Clients MUST anticipate other, unrelated uses of
postMessage and ignore unrecognized messages not conforming to the protocol.
[DD-20]
4.4 Prefill
Servers MAY support prefill for creation and/or selection dialogs. Client provided prefill information, either
in a request entity body or query parameters is intended to inform servers of possible initial values for
creation dialogs, or the preferred content of selection dialogs. Clients SHOULD NOT assume any specific
content or URL format.
[DD-21]
Servers MAY allow clients to prefill dialogs by accepting HTTP POST requests where the Request-URI is the
dialog descriptor and the entity body is an entity describing the initial values.
[DD-22]
Servers that support prefill MUST include the value
POST in the set of Allow header values returned in response to HTTP OPTIONS requests
for the dialog descriptor URI.
[DD-23]
Example 26
Allow: GET,POST,HEAD,OPTIONS
Servers MAY describe prefill constraints by adding an
oslc:resourceShape property to the dialog descriptor whose value is a
resource shape URI.
[DD-24]
Servers MUST NOT reject prefill requests on creation dialogs solely because they are missing required fields
for the resource. Users can fill in the missing values in the dialog.
[DD-25]
On successful prefill requests, servers MUST respond with status code 201 (Created) and a
Location header whose value is the URI of the prefilled dialog.
[DD-26]
After some elapsed time, servers MAY respond with a 404 (Not Found) or 410 (Gone) to an HTTP GET request for a
prefilled dialog URI.
[DD-27]
Servers MAY support prefill by adding initial values as query parameters to the delegated dialog URI. Clients
SHOULD NOT assume any specific URL format, however.
[DD-28]
5. Resource Constraints
This document applies the following constraints to the Core vocabulary terms.
An OSLC server providing Dialog capability MUST implement the vocabulary defined in this section.
[DD-29]
Summary: Describes information about a dialog such as its title and dimensions.
Dialog Properties
Prefixed Name
Occurs
Read-only
Value-type
Representation
Range
Description
dcterms:title
Exactly-one
true
XMLLiteral
N/A
Unspecified
Title string that could be used for display.
oslc:dialog
Exactly-one
true
unspecified
Either
Unspecified
The URI of the dialog.
oslc:hintHeight
Zero-or-one
true
unspecified
Either
Unspecified
Recommended height of the dialog. Values are expressed using length units as specified in [CSS21].
oslc:hintWidth
Zero-or-one
true
unspecified
Either
Unspecified
Recommended width of the dialog. Values are expressed using length units as specified in [CSS21].
oslc:label
Zero-or-one
true
string
N/A
Unspecified
Very short label for use in menu items.
oslc:resourceShape
Zero-or-many
true
Resource
Reference
oslc:ResourceShape
Describes constraints on dialog prefill requests.
oslc:resourceType
Zero-or-many
true
Resource
Reference
rdfs:Class
The expected resource type URI for the resources that will be returned when using this dialog. These would be the URIs found in the result resource's rdf:type property.
oslc:usage
Zero-or-many
true
Resource
Reference
Unspecified
An identifier URI for the domain specified usage of this dialog. If a resource has multiple uses, it may designate the primary or default one that should be used with a property value of oslc:default.
6. Conformance
Implementations of this specification need to satisfy the following conformance clauses.
In responses to HTTP GET requests targeting resources that have dialogs, servers SHOULD either include a
Vary response header with at least Accept and Prefer field values or a
Cache-Control header value no-store.
Servers MAY also provide delegated dialog discovery using the
ServiceProvider and
Service resource and the oslc:creationDialog and
oslc:selectionDialog properties.
Servers MAY support other protocols for dialog responses not specified in this document, which clients request
by appending a fragment identifier [RFC3986] describing the protocol to the end of the dialog URI.
Servers MUST use postMessage for dialog responses if a client has not added a fragment identifier
to the dialog URI, or the fragment identifier is #oslc-core-postMessage-1.0.
Servers MAY support prefill for creation and/or selection dialogs. Client provided prefill information, either
in a request entity body or query parameters is intended to inform servers of possible initial values for
creation dialogs, or the preferred content of selection dialogs. Clients SHOULD NOT assume any specific
content or URL format.
Servers MAY allow clients to prefill dialogs by accepting HTTP POST requests where the Request-URI is the
dialog descriptor and the entity body is an entity describing the initial values.
Servers that support prefill MUST include the value
POST in the set of Allow header values returned in response to HTTP OPTIONS requests
for the dialog descriptor URI.
Servers MUST NOT reject prefill requests on creation dialogs solely because they are missing required fields
for the resource. Users can fill in the missing values in the dialog.
On successful prefill requests, servers MUST respond with status code 201 (Created) and a
Location header whose value is the URI of the prefilled dialog.
Servers MAY support prefill by adding initial values as query parameters to the delegated dialog URI. Clients
SHOULD NOT assume any specific URL format, however.
An OSLC server providing Dialog capability MUST implement the vocabulary defined in this section.
Appendix A. Dialog Results JSON
Dialog results are represented as JSON [RFC4627]. The top-level JSON object has an
oslc:results property.
Property
Type
Occurs
Description
oslc:results
JSON Array
Exactly-one
An array of results, each result a JSON object. An empty array means the user canceled the dialog or
didn't select a resource.
Each result is a JSON object with the following properties.
Property
Type
Occurs
Description
rdf:resource
String
Exactly-one
URI of the resource selected or created
oslc:label
String
Zero-or-one
Short label describing the resource selected
Here is an example response that contains two resources.
Example 27
{"oslc:results":[{"oslc:label":"Bug 123: Server crash","rdf:resource":"http://example.com/bug123"},{"oslc:label":"Bug 456: Client hangs on startup","rdf:resource":"http://example.com/bug456"}]}
When sent as a message in calls to postMessage, the JSON string is prefixed with the characters
oslc-response:.
