Because BackendTask's in elm-pages never run in the browser (see the BackendTask docs), you can access environment variables securely. As long as the environment variable isn't sent down into the final Data value, it won't end up in the client!

import BackendTask exposing (BackendTask)
import BackendTask.Env
import Exception exposing (Throwable)


type alias EnvVariables =
    { sendGridKey : String
    , siteUrl : String
    }


sendEmail : Email -> BackendTask Throwable ()
sendEmail email =
    BackendTask.map2 EnvVariables
        (BackendTask.Env.expect "SEND_GRID_KEY" |> BackendTask.throw)
        (BackendTask.Env.get "BASE_URL"
            |> BackendTask.map (Maybe.withDefault "http://localhost:1234")
        )
        |> BackendTask.andThen (sendEmailBackendTask email)


sendEmailBackendTask : Email -> EnvVariables -> BackendTask Throwable ()
sendEmailBackendTask email envVariables =
    Debug.todo "Not defined here"

Errors