Fish Plugin: How to define variables and import them in a different file

I want to define the following variables: URL, Username and Password in variables.fish and then import and use it. Since this way I would just need to configure it at one place instead of modifying each and every app I'm stumped on how to do this File structure is currently like this

└── functions
    │── variables.fish
    │   └── variables like URL, username and password
    │── proxy.fish
    │   └── handler function
    │── apps
    │   └── all the app specific logic goes here
    └── utils 
        └── helper functions: pretty printing etc.

Any pointers would be appreciated thanks!