Most of the user interface involves Spring MVC “views”, which are rendered with a templating engine theoretically chosen from a number of supported options. While this is extensible, the three view resolvers installed by default, in order, are:
BeanNameViewResolver – used rarely for some internal reasons, it resolves a view against a bean of the same name in the Spring context
VelocityViewResolver – the most commonly used, supports the Velocity template engine used in other places in the IdP
InternalResourceViewResolver – a fallback that relies on JSP/JSTL templates, mainly used for the IdP’s status page
Virtually of the views supplied with the software right now are Velocity templates (with a “vm” extension). A handful are installed by default because they are core functionality and not installed by a specific Module. The rest are installed as specific modules that manage them are enabled. For example the “login form” consists of a couple of views that are actually part of the Password login flow, which is enabled by default.
When Spring looks for a view template, it will search for one with the “vm” extension in the location(s) specified by the idp.views property, and if it can’t locate one, it will search inside the war within WEB-INF/jsp for a template with the “jsp” extension and run that instead.
In the future, we intend to support other view technologies by means of plugins and may eventually move Velocity support itself into such a plugin to insulate the IdP further, but for the life of this major version, the above is accurate.
Look and Feel
The main purpose of the supplied templates is to define the necessary form submission / link interface contracts required for proper functionality of the various features. In some cases, the views render information from the IdP to the user (e.g., the Consent features) while in others they merely collect information from the user. Logout is the most complex case, and has a bit of both.
The actual look and feel of the views is not in general expected to meet anybody’s needs in particular. Deployers are not only encouraged but expected to change them fairly extensively in most cases. The goal of the installation process is to ensure that functionality is usable and can be tested or demonstrated before the work of aligning the look and feel to meet local expectations is done.
Defaults aside, do NOT use the delivered style sheet or image filenames in production, and always adjust the relevant values in messages/messages.properties to reflect your own chosen names for these files (or replace the use of the properties entirely):
While the original style sheets and images will not be overwritten by upgrades, the properties that refer to them could have their default values changed, which could alter the appearance of your pages if you haven’t defined values for them yourself to supplant the system values.
A sample logo is installed to edit-webapp/images/placeholder.png and is referenced by default via the message property idp.logo
All views link to a style sheet installed to edit-webapp/css/placeholder.css; this is referenced by default via the message property idp.css
Upgrades are meant to be safe, but prior to V4.2, the default CSS and logo files (which were strictly provided as examples) have been overwritten during upgrades. This is no longer true, but please heed the caution box above: do NOT rely on the default filenames for your “final” configuration. Even if you make use of the provided CSS, copy it to a filename of your own and set the idp.css property to switch to it.
Content Security Policy
This section refers to features added in V5.1.
The IdP has generally made limited use of CSP, which is a quite complex specification designed to allow web servers to signal to clients to disallow various sorts of content that attackers may be able to inject into pages using various exploits. V5.1 has introduced a number of changes to the default view templates, and adds a number of built-in objects to the Spring environment and to the views to facilitate relatively simple CSP additions to views to lock them down without requiring the very complex step of exbedding and expressing inline event handlers as declarative script blocks.
Use in OpenSAML Binding Templates
While many deployers may override them, by default the templates used to carry SAML messages in forms for the non-redirect-based bindings are internal to the OpenSAML library. To allow use (or non-use) of CSP with the default templates, the idp.encoders.cspEnabled property was added to control this. It does default to true, so has to be set to false by hand to disable the new feature. Depending on how much of the templates are overridden, the property may or may not be applicable or effective.
Use in Views
shibboleth.CSPNonceGenerator – this is an IdentifierGenerationStrategy (an interface in our API) whose generateIdentifier() method will produce an adequately random value to use as a nonce.
Hash Example in Velocity
This example comes from the default login.vm template:
The particular rule would generally be “script-src-attr” when the script is used in an HTML attribute, or “script-src-elem” in the less common case of a <script> element. (Generally nonces work better for script blocks.)
As the example shows, changing the script in some way would only require changing the text in the #set macro, because the hash is computed against whatever is found in that variable. Later on the variable would be used to embed the script into the desired spot in the template.
Nonce Example in Velocity
When hashes are too unwieldy to use, nonces are usually the best fallback, and work well for scripts, particularly external ones. Nonces are generated and then added to both a header at the top of a view and in a nonce attribute in the <script> element: