Unable to post forms that exceed the 4096 bytes size limit in Bamboo

For example, in Bamboo version 9.2.7, customers are unable to store 8192-bit SSH keys in the Shared credentials. We receive the error message "SSH Key can not be empty" while saving the key. 

There are no issues with storing 4096 bit or lower SSH key.

How to reproduce:

1. Navigate to Bamboo Administration > Overview > Build Resources > Shared credentials.
2. Click on Add new credentials > SSH.
3. Provide a Credential name and enter the 8192-bit SSH key in the SSH key section. 
4. provide the SSH passphrase (if applicable)
5. Click Save credentials.

Expectation

Saves the 8192-bit SSH key.

Actual

An error message "SSH key can not be empty" can be seen on the Add new SSH credentials pop-up window.

Workaround

The issue is caused by an update to a third-party library Apache Struts that had imposed a hard limit on form sizes. New versions of Bamboo listed on the "Fix Version/s" field on this bug will contain an increased limit that will overcome that limitation.

As a workaround, modify the <bamboo-install>/atlassian-bamboo/WEB-INF/classes/struts.properties file, add a line as the one below and restart Bamboo.

# Override default string length limit of 4096, which is too short for Bamboo; set it to 10kb
struts.multipart.maxStringLength=10240