Slack has deprecated TLS versions 1.0 and 1.1. We received an email stating on March 4th of 2020 that those versions will be sunset and only TLS 1.2 and up will be supported. We are concerned that the add-on we're using will not work and will require an update from the developer. Is this something being taken into account? Do we need to upgrade from 1.5.8 to ensure no interruption of service?
I've added the plugin tag for that particular Bamboo plugin to your question, in hopes that the plugin author might see it.
In general, Java 8 and above support TLS 1.2. If the plugin is using the standard Java libraries to establish its TLS connection, you should be in good shape. We began support for Java 8 with Bamboo 5.8 back in 2015 - assuming you're running a version newer than that and either used the Windows installer or have an up-to-date system Java, you should be in good shape with Java 8 support.
I'm guessing it was you who created this issue directly on the plugin's repo 😁- after looking through the plugin source, the standard org.apache.http library is being used for the connection. Assuming again that you're on Java 8 or above, I think TLS 1.2 should be supported with the plugin.