Integrate with Password Managers
Most password managers already have the ability to save the URLs for all of your passwords.
If you can create an integration with things like Keeper, LastPass, Roboform, Dashlane, BitWarden, LogmeOnce, Password Boss, 1Password, etc, it would be a very powerful integration.
The idea is to read from the PW manager for all the links they already have, without touching the credentials. Then just import all the links into your tool directly, so that they automatically launch the link from the PW manager, automatically invoking the right login credential.
Or conversely, just helping to organize the many links in a PW manager to match up with what has been organized in Raindrop.io automatically.