Officially provide support for internal and external base url for JIRA

Problem Definition

There is currently no official way to configure JIRA with two url and it is very common for organizations to have one internal and one external url.

It is currently only possible to configure one baseurl and this is mentioned in our documentation :

1. https://confluence.atlassian.com/upm/diagnosing-base-url-configuration-problems-273875734.html
2. https://confluence.atlassian.com/adminjiraserver/configuring-jira-application-options-938847824.html

The base URL of this Jira installation. You can only configure Jira to respond to a single URL and this setting must match the URL that your users request for accessing your Jira instance. You cannot (for example) have a different hostname or URL for internal and external users.

Suggested Solution

Provide the functionality and official documentation on how to configure JIRA with internal and external or more than one url.

Notes

While one can configure multiple Tomcat connectors with different URLs, due to the nature of our current OAuth implementation signing requests with the base URL setting ( see https://docs.atlassian.com/DAC/javadoc/applinks/3.6.1/reference/com/atlassian/applinks/core/auth/oauth/RequestUtil.html ), using a different URL other than the base url will break integrations relying on OAuth for authentication