Extract user utility code into own module

This provides more room for expansion, and reduces the amount of
arbitrary code in the __init__.py file for the new package.

app/utils/user.py

@@ -0,0 +1,68 @@
+import os
+from functools import wraps
+
+from flask import abort, current_app
+from flask_login import current_user, login_required
+
+from app.notify_client.organisations_api_client import organisations_client
+
+user_is_logged_in = login_required
+
+
+with open('{}/email_domains.txt'.format(
+    os.path.dirname(os.path.realpath(__file__))
+)) as email_domains:
+    GOVERNMENT_EMAIL_DOMAIN_NAMES = [line.strip() for line in email_domains]
+
+
+def user_has_permissions(*permissions, **permission_kwargs):
+    def wrap(func):
+        @wraps(func)
+        def wrap_func(*args, **kwargs):
+            if not current_user.is_authenticated:
+                return current_app.login_manager.unauthorized()
+            if not current_user.has_permissions(*permissions, **permission_kwargs):
+                abort(403)
+            return func(*args, **kwargs)
+        return wrap_func
+    return wrap
+
+
+def user_is_gov_user(f):
+    @wraps(f)
+    def wrapped(*args, **kwargs):
+        if not current_user.is_authenticated:
+            return current_app.login_manager.unauthorized()
+        if not current_user.is_gov_user:
+            abort(403)
+        return f(*args, **kwargs)
+    return wrapped
+
+
+def user_is_platform_admin(f):
+    @wraps(f)
+    def wrapped(*args, **kwargs):
+        if not current_user.is_authenticated:
+            return current_app.login_manager.unauthorized()
+        if not current_user.platform_admin:
+            abort(403)
+        return f(*args, **kwargs)
+    return wrapped
+
+
+def is_gov_user(email_address):
+    return _email_address_ends_with(
+        email_address, GOVERNMENT_EMAIL_DOMAIN_NAMES
+    ) or _email_address_ends_with(
+        email_address, organisations_client.get_domains()
+    )
+
+
+def _email_address_ends_with(email_address, known_domains):
+    return any(
+        email_address.lower().endswith((
+            "@{}".format(known),
+            ".{}".format(known),
+        ))
+        for known in known_domains
+    )