OAuth Support (#53)

Rips out the old auth method, adds OAuth support. Fixes #51.

Tested Platforms:
- [x] Linux
    - [x] Flatpak
    - [x] Native (Nix)
- [x] Android
- [ ] Windows
- [ ] MacOS

Reviewed-on: Nexus/nexus#53

macos/Runner/Info.plist

@@ -28,5 +28,18 @@
 	<string>MainMenu</string>
 	<key>NSPrincipalClass</key>
 	<string>NSApplication</string>
+	<key>CFBundleURLTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleURLName</key>
+			<!-- abstract name for this URL type (you can leave it blank) -->
+			<string>auth_callback</string>
+			<key>CFBundleURLSchemes</key>
+			<array>
+				<!-- your schemes -->
+				<string>nexus.federated.nexus</string>
+			</array>
+		</dict>
+	</array>
 </dict>
 </plist>