nextcloud oauth (#10562)

Fix #7078

vendor/github.com/markbates/goth/providers/nextcloud/README.md

@@ -0,0 +1,85 @@
+# Nextcloud OAuth2
+
+For this backend, you need to have an OAuth2 enabled Nextcloud Instance, e.g.
+on your own private server.
+
+## Setting up Nextcloud Test Environment
+
+To test, you only need a working Docker image of Nextcloud running on a public
+URL, e.g. through [traefik](https://traefik.io/)
+
+```docker-compose.yml
+version: '2'
+
+networks:
+  traefik-web:
+    external: true
+
+services:
+  app:
+    image: nextcloud
+    restart: always
+    networks:
+      - traefik-web
+    labels:
+      - traefik.enable=true
+      - traefik.frontend.rule=Host:${NEXTCLOUD_DNS}
+      - traefik.docker.network=traefik-web
+    environment:
+      SQLITE_DATABASE: "database.sqlite3"
+      NEXTCLOUD_ADMIN_USER: admin
+      NEXTCLOUD_ADMIN_PASSWORD: admin
+      NEXTCLOUD_TRUSTED_DOMAINS: ${NEXTCLOUD_DNS}
+```
+
+and start it up via
+
+```
+NEXTCLOUD_DNS=goth.my.server.name docker-compose up -d
+```
+
+afterwards, you will have a running Nextcloud instance with credentials
+
+```
+admin / admin
+```
+
+Then add a new OAuth 2.0 Client by going to
+
+```
+Settings -> Security -> OAuth 2.0 client
+```
+
+![Nextcloud Setup](nextcloud_setup.png)
+
+and add a new client with the name `goth` and redirection uri `http://localhost:3000/auth/nextcloud/callback`. The imporant part here the
+two cryptic entries `Client Identifier` and `Secret`, which needs to be
+used in your application.
+
+## Running Login Example
+
+If you want to run the default example in `<goth>/examples`, you have to 
+retrieve the keys described in the previous section and run the example
+as follows:
+
+```
+NEXTCLOUD_URL=https://goth.my.server.name \
+NEXTCLOUD_KEY=<your-key> \
+NEXTCLOUD_SECRET=<your-secret> \
+SESSION_SECRET=1 \
+./examples
+```
+
+Afterwards, you should be able to login via Nextcloud in the examples app.
+
+## Running the Provider Test
+
+The test has the same arguments as the login example test, but starts the test itself
+
+```
+NEXTCLOUD_URL=https://goth.my.server.name \
+NEXTCLOUD_KEY=<your-key> \
+NEXTCLOUD_SECRET=<your-secret> \
+SESSION_SECRET=1 \
+go test -v
+```