We allow users to change the regular expression that defines a project key in JIRA. This could result in project keys where the key includes a slash such as: JRA/PROJECT.

This does not work. Even if we encode the slash as a percent octet, most application servers will decode it anyway, which makes it impossible for the Quicklinkservlet to determine what's part of the project key and what's not. This is in line with the URL spec, in particular:

The purpose of reserved characters is to provide a set of delimiting characters that are distinguishable from other data within a URI. URIs that differ in the replacement of a reserved character with its corresponding percent-encoded octet are not equivalent. Percent-encoding a reserved character, or decoding a percent-encoded octet that corresponds to a reserved character, will change how the URI is interpreted by most applications. Thus, characters in the reserved set are protected from normalization and are therefore safe to be used by scheme-specific and producer-specific algorithms for delimiting data subcomponents within a URI.

We'll have to add a clear comment to jira-application.properties to warn users that they should not allow / in project keys!