Add error 100 message

[v0idzz]

From my testing, error 100 happens when either digest or signature headers have invalid values.

[kuba2k2]

What is the message returned by the server in case of this error code?

[v0idzz]

The message is Użytkownik nie jest uprawniony do przeglądania żądanych danych: <base64_string> where the base64_string can be decoded to: <canonical_url><some_other_base64_value><gmt_timestamp>. For example: api%2fmobile%2fregister%2fnew<base64_val_redacted>Sat, 16 Oct 2021 09:06:07 GMT.

Due to the fact I am unsure what the other base64 value is, I redacted it. Either way it surely is not a UTF-8 string.

[kuba2k2]

Oh, okay. What happens if you try to access for example some other student's data?
I'm asking as I think I remember the error code 100 in more different situations, which would mean the exception's message needs to be more generic.

[kuba2k2]

Yup, just checked it. When trying to access a different pupilId, the error is Użytkownik nie jest uprawniony do przeglądania żądanych danych, but without the Base64 string. For now, your solution in the API may be confusing, as it always returns a signature error.
I think checking for the presence of the B64 string should be enough, for now.

[v0idzz]

This should do the job.