Comment 1 for bug 1876169

After the research the patch was made as proof-of-concept to enable vault webui (attached)
However it seems that the vault binary we use does not support UI option.

ubuntu@juju-902b45-13:~$ curl -L http://127.0.0.1:8200/ui
...
 <h1>Vault UI is not available in this binary.</h1>
 </div>
 <p>To get Vault UI do one of the following:</p>
 <ul>
 <li><a href="https://www.vaultproject.io/downloads.html">Download an official release</a></li>
 <li>Run <code>make bin</code> to create your own release binaries.
 <li>Run <code>make dev-ui</code> to create a development binary with the UI.
...

So far it seems we must abandon that or keep it in the wishlist.
After resolving there we would need to add relevant functional test to check whether the endpoint runs UI.