messages keeps asking for password for jabber account
This solution worked for me:
https://discussions.apple.com/message/32744059#32744059


  After running a comparison with a working version (on Sierra 10.12.6) it looks like the solution (at least for me) is to change the Where value that gets generated on sign in from what gets populated when adding an account in High Sierra com.apple.account.jabber.password to Jabber
  
  In order to make this change follow these steps:
  
  
  Open Keychain Access
  Search for com.apple.account.jabber.password
  Double click it to open the attributes prompt
  In the Where field (fourth one down) you should see com.apple.account.jabber.password
  Replace all text in that field with Jabber
  Click Save Changes
  
  
  After making this change the first launch of messages asked me to allow permission to access keychain. After doing so any subsequent open of messages works as expected.