GovDelivery.md

Newsletter signup in the sitewide header

The 'keep me posted' button reveals a slide-down panel which allows visitors to enter their email address to subscribe to emails using the GovDelivery service. The following process determines how it appears:

1. The page template loads govdelivery.js. For example, on WebForms pages desktop.master loads scriptsdesktop.ascx, which specifies the Email script, which resolves to govdelivery.js in web.config. It loads the govdelivery-button-*.css files by a similar method.
2. govdelivery.js checks that it is on the https protocol on one of its approved domains. If so, it inserts the 'Keep me posted' button in the header. This picks up the CSS already loaded.
3. When the 'Keep me posted' button is clicked, it makes a request for govdelivery.html, inserts it into the page, and slides down the panel to reveal it. However, this request is intercepted by CorsForStaticFilesHandler which is registered in web.config to handle *.html requests in the controls folder. CorsForStaticFilesHandler checks the origin of the request against a list of approved domains in web.config and, if there is a match, inserts the appropriate CORS header. This allows the request to succeed across different domains and subdomains.
4. govdelivery.html has a form which posts to the GovDelivery site, at which point that service takes over.