This is a request for support regarding JSON token creation for MapKit JS.
Since my intent is not to create an app, but only to use MapKit JS, I only need a single JSON authorization token. That should not require use of a code library.
Following the instructions at "https://developer.apple.com/documentation/mapkitjs/creating_a_maps_identifier_and_a_private_key",
I have created a Maps ID and obtained a MapKit JS Private Key (a .p8 file). That key is downloaded and stored in a safe place.
However, there are NO instructions from Apple on how to use that private key.
The downloaded file is not of a type that is recognized by MacOS, so it cannot be opened with a double-click.
By experimentation, I discovered that it is possible to open the private key file using TextEdit. This revealed that the file is plain text, with 200 characters of encoded material preceded by a "begin" line and followed by an "end" line.
Proceeding to the documentation page at "https://developer.apple.com/documentation/mapkitjs/creating_and_using_tokens_with_mapkit_js",
the instructions to "Create a MapKit JS Token" are woefully incomplete. It is simple enough to complete a JSON object header and a JSON object claims payload with the necessary details appropriate to my situation. (However, it did take some experimentation at jwt.io/#debugger to determine reasonable values for "iat" and "exp".) But there is no clue anywhere as to how to "use [my] private key to sign the token", and all experimentation at jwt.io/#debugger has failed, i.e., yielded "invalid signature" instead of an encoded token.
Note that jwt.io/#debugger does not provide any instructions or help; it is one of those things that is supposed to be "intuitively obvious," but isn't.
What do I need to do to use the private key that Apple provided to sign a JSON token that I can then use with MapKit JS?