Add Login.gov *\o/*

This commit incldues a wrapper application which handles
the Private Key JWT method of authenticating via OpenID
Connect using the underlying pyoidc library.

src/djangooidc/exceptions.py

@@ -0,0 +1,46 @@
+from oic import rndstr
+from http import HTTPStatus as status
+
+
+class OIDCException(Exception):
+    """
+    Base class for django oidc exceptions.
+    Subclasses should provide `.status` and `.friendly_message` properties.
+    `.locator`, if used, should be a useful, unique identifier for
+    locating related log messages.
+    """
+    status = status.INTERNAL_SERVER_ERROR
+    friendly_message = "A server error occurred."
+    locator = None
+
+    def __init__(
+        self,
+        friendly_message=None,
+        status=None,
+        locator=None
+    ):
+        if friendly_message is not None:
+            self.friendly_message = friendly_message
+        if status is not None:
+            self.status = status
+        if locator is not None:
+            self.locator = locator
+        else:
+            self.locator = rndstr(size=12)
+
+    def __str__(self):
+        return f"[{self.locator}] {self.friendly_message}"
+
+
+class AuthenticationFailed(OIDCException):
+    status = status.UNAUTHORIZED
+    friendly_message = "This login attempt didn't work."
+
+
+class InternalError(OIDCException):
+    status = status.INTERNAL_SERVER_ERROR
+    friendly_message = "The system broke while trying to log you in."
+
+
+class BannedUser(AuthenticationFailed):
+    friendly_message = "Your user is not valid in this application."