Login in Cypress without hardcoding

I don’t know how to rewrite this syntax correctly, because I get an error like “Invalid left-hand side in assignment expression.”

Cypress.Commands.add('logintest', (env,username) => {
    env(staging) = cy.visit('link')
    env(live) = cy.visit('link') 

    username (userone =
      cy.get('input[name="Parameter.UserName"]').type('userone'),
      cy.get('input[name="Parameter.Password"]').type('password')
    )
})