Issue Summary

Application links between two separate Atlassian sites will fail the OAuth setup if sites are using custom domains. 

Steps to Reproduce

1. Create two separate sites with custom domains
2. In site one, add the Jira product
3. In site two, add the Confluence product 
4. Create an applink between the two products. The applink setup should be successful at this stage.

1. 1. The failure occurs when the user attempts the OAuth process when using features in the each product
   2. For example trying to link a Confluence page to a Jira work item

Expected Results

• Because the applink setup succeeds, utilizing the Confluence page/work item linkage should also succeed
• Alternatively, because applinks do not support custom domains, another expected result is displaying an error when attempting the applink setup. 

Actual Results

When the user attempts linking the Jira work item to the Confluence page on the remote site, they will be prompted to complete the OAuth process for the applink. At this stage, they will encounter an OAuth error even if they have successfully logged into both the Jira/Confluence products. 

Workaround

It may be possible to retrigger the OAuth process and resolve identity errors by taking the following steps:

1. After encountering the "Authentication failed" message, head back on the Jira work item
2. Select the "Link Page" option again
3. Manually attempt to enter a valid Confluence page, which can trigger a message: "Authenticate with Confluence to see this page". If the message appears, click it to retrigger the OAuth process and allow Confluence to access Jira