Security
Your Bitbucket Password
You will be asked to provide the password you use to log in to Bitbucket every time you start Bittray.
It will not be stored.
Security
The WCM is not a secure password store by default.
In order to securely store the password in the WCM (or registry, or anywhere) in a retrievable form, it would need to be encrypted using a passphrase provided by the user.
The user would need to enter that decryption passphrase every time Bittray launched to decrypt the stored Bitbucket
credentials.
So you’d have to enter a password every time you launch anyway, saving no effort.
Storing it is arguably actively harmful.