Feature: PKI for JWT (#24)

* [feat] Add support for PKI algorithms when signing JWT
* [feat] Add config options for key-pair and the passphrase for private key
* [docs] Update docstrings
* [refactor] Fix error codes and updated them with the latest changes
* [feat] Add cryptography dependency to load encrypted private keys if there's a passphrase
* [refactor] Separate error handling on different config options: algorithm, secret, etc.
* [test] Add parametrized tests for PKI changes for signing JWT
* [refactor] Add type-checking to prevent TypeErrors if passphrase is passed as bytes
* [refactor] Remove default_backend, because the parameter is ignored (probably obsolete)
* [docs] Convert and update readme and authors
* [docs] Add instructions for enabling PKI for JWT and install cryptography dep.
* [tools] Update setup.py to include extra requirements (cryptography)
* [tools] Update version to 3.3.0
* [tools] Fix readme file ext
* [tools] pysaml2 already installs cryptography package
* [refactor] JWT_ALGORITHM decides which algorithm to use if all fields are present
* [docs] Update readme to reflect changes
* [docs] Update explanations section with a table containing extra info like data type, default value and example(s)
* [refactor] Extract validations into separate functions and address comments
* [docs] Update readme with signing algorithm and more detailed instructions
* [refactor] Fix error message
* [refactor] Make errors more generic
* [refactor] Remove unnecessary code and comments
* [refactor] Remove unnecessary variable

Author: mostafa

AUTHORS.md

@@ -0,0 +1,52 @@
+This project is currently maintained by Mostafa Moradian and various contributors:
+
+# Django SAML2 Auth
+
+- Original author:
+  - [Li Fang](https://github.com/fangli)
+
+- Current maintainer:
+  - [Mostafa Moradian](https://github.com/mostafa) (k6.io & Grafana Labs)
+
+# Dependencies
+
+PySAML2: [c00kiemon5ter](https://github.com/c00kiemon5ter) and other contributors.
+
+PyJWT: [José Padilla](https://github.com/jpadilla) (Auth0) and other contributors.
+
+cryptography: [Paul Kehrer](https://github.com/reaperhulk) and other contributors.
+
+dictor: [perfecto25](https://github.com/perfecto25) and other contributors.
+
+# Test dependencies
+
+django: [various contributors](https://github.com/django/django/blob/master/AUTHORS).
+
+pytest: Holger Krekel and [other contributors](https://github.com/pytest-dev/pytest/blob/master/AUTHORS).
+
+pytest-django: Ben Firshman, Andreas Pelme and [other contributors](https://github.com/pytest-dev/pytest-django/blob/master/AUTHORS).
+
+responses: [markstory](https://github.com/markstory) and other contributors.
+
+# Contributors
+
+If your code or changes are here, but you are not mentioned, please open
+an issue.
+
+- [Mostafa Moradian](https://github.com/mostafa) (k6.io & Grafana Labs)
+- [DSpeichert](https://github.com/DSpeichert)
+- [jacobh](https://github.com/jacobh)
+- [Gene Wood](http://github.com/gene1wood/)
+- [Terry](https://github.com/tpeng)
+- [Tim Pierce](https://github.com/qwrrty/) (Adobe Systems)
+- [Tonymke](https://github.com/tonymke/)
+- [pintor](https://github.com/pintor)
+- [BaconAndEggs](https://github.com/BaconAndEggs)
+- [Ryan Mahaffey](https://github.com/mahaffey)
+- [ayr-ton](https://github.com/ayr-ton)
+- [kevPo](https://github.com/kevPo)
+- [chriskj](https://github.com/chriskj)
+- [Griffin J Rademacher](https://github.com/favorable-mutation)
+- [Akshit Dhar](https://github.com/akshit-wwstay)
+- [Jean Vincent](https://github.com/jean-sh)
+- [Søren Howe Gersager](https://github.com/syre)