[Bug] While upgrading Jira Service Desk with expired license, new license cannot be applied

[Graham Leggett]

Having upgraded to Jira Service Desk v7.4.1 from a version in the v6.4 range, the software fails to come up with the following message:

2017-07-30 23:05:14,492 JIRA-Bootstrap ERROR      [c.a.jira.health.HealthChecks] Your current JIRA Service Desk license doesn't allow you to upgrade to this version of JIRA (7.4.1). JIRA Service Desk 
expired on 17/Mar/17 1:00 PM, and you can currently only upgrade to versions released prior to this date. Alternatively you can renew your license at my.atlassian.com (http://my.atlassian.com) which w
ill allow you to upgrade to this version of JIRA (7.4.1). You can enter your new license here (/secure/ConfirmNewInstallationWithOldLicense!default.jspa).
    See our documentation for more information on licensing errors.

According to the above error message, adding the license should be achieved by visiting /secure/ConfirmNewInstallationWithOldLicense!default.jspa

Attempting to do this causes a redirect to /secure/errors.jsp, which breaks because JIRA is hosted below /jira on this installation.

Visiting the opening JIRA page should cause you to go to the licensing screen (in theory), but in practice it leads you to a pagethat says "Oops, you've found a dead link."

How is it possible to apply a license to JIRA when the JIRA user interface has stopped working?