TypeScript tries to make sure the variables are always populated with data of the type specified during the variable definition.
Issue
When the TypeScript compiler thinks a function can return another data type, or “unknown”, “undefined”, “null”, Visual Studio Code displays a warning:
type ‘unknown’ is not assignable to type …
Solution
The solution is to explicitly convert the return type to the expected one:
let soObject: SsoObject = <SsoObject> decodeJWT(ssoCookie);