decodeToken parses the token, checking that it meets the Jwt standards.

decodeToken dec token

In the event of success, decodeToken returns an Elm record structure using the JSON Decoder.

`Checks whether a token has expired, and returns True or False, or any error that occurred while decoding the token.

Note: This function assumes that the expiry was set in seconds and thus multiplies by 1000 to compare with Javascript time (in milliseconds). You may need to write a custom version if your server-side Jwt library works differently.

authenticate is a standard Http POST method containing login credentials, and using a json decoder to extract the returned token.

submitCredentials : Model -> Cmd Msg
submitCredentials model =
    E.object
        [ ("username", E.string model.uname)
        , ("password", E.string model.pword)
        ]
    |> authenticate Auth "/sessions" tokenStringDecoder

createRequest creates a Http.Request with the token added to the headers, and sets the withCredentials field to True.

get is a replacement for Http.get that returns a Http.Request with the token attached the headers.

Task.perform
    PostFail PostSucess
    (get token dataDecoder "/api/data")

get_ takes the same parameters as get, but returns a Task where a 401 Unauthorized error due to token expiry has been converted into a TokenExpired.

update ... =
GetResult (Result.Err err) ->
    case err of
        Jwt.TokenExpired ->
            { model | msg = "Token expired" } ! []
        _ ->
            { model | msg = toString err } ! []


[...]
tryToken : String -> Cmd Msg
tryToken token =
    Jwt.get_ token "/api/data" dataDecoder
    |> Task.perform GetResult

post is a replacement for Http.post that attaches a provided Jwt token to the headers.

put provides Http.put with the token attached to the headers.

Examines a 401 Unauthorized reponse, and converts the error to TokenExpired when that is the case.

getAuth : Token -> String -> Json.Decoder a -> Task Never (Result JwtError a)
getAuth token url dec =
    createRequest "GET" token url dec Http.emptyBody
    |> toTask
    |> Task.map Result.Ok
    |> Task.onError (promote401 token)

We distinguish between various errors

• From Http.Error. We pass these straight through unless using promote401,
• 401 (Unauthorized) errors, due either to token expiry or some other reason
• issues with processing (e.g. base 64 decoding) the token, and
• problems decoding the json data within the content of the token