package Ġcom . sh in wan 2 . post maker . domain . auth Ċ Ċ import Ġio . reactivex . Comp letable Ċ import Ġio . reactivex . Observable Ċ Ċ interface ĠAuthentication Service Ġ{ ĊĠĠĠ Ġval ĠuserId : ĠString ? ĊĠĠĠ Ġfun Ġsign In ( email : ĠString , Ġpassword : ĠString ): ĠComp letable ĊĠĠĠ Ġfun Ġsign Up ( email : ĠString , Ġpassword : ĠString ): ĠComp letable ĊĠĠĠ Ġfun Ġsign Out (): ĠComp letable ĊĠĠĠ Ġfun Ġis Signed In ( userId : ĠString ? Ġ= Ġnull ): ĠBoolean ĊĠĠĠ Ġfun Ġauth StateChanged (): ĠObservable < Boolean > Ċ } Ċ