Set up cron container to access back end services

(from ChatGPT)

To run a cron job in a container that interacts with your backend services and needs to authenticate using a JWT from Keycloak (without a logged-in client), you can use Keycloak's client credentials flow. This flow allows a service (like a cron job or any other non-interactive system) to authenticate with Keycloak and obtain a token without needing a user to log in.

Here’s how you can achieve this:

1. Create a Service Account in Keycloak

In the Keycloak admin console, go to your realm, then navigate to Clients.
Create a new client or use an existing one.
Enable Service Accounts for this client:
- Under the client’s settings, set Access Type to confidential.
- Enable the Service Accounts Enabled option.
Save the client configuration.

2. Configure Client Credentials for the Service Account

Go to the Credentials tab of the client.
Generate a client secret. This secret will be used to authenticate the cron job to Keycloak.

3. Use the Client Credentials Flow to Obtain a Token

In your cron job container, you can make an HTTP request to Keycloak’s token endpoint to get an access token using the client credentials flow.

Here's an example of how to get a token using curl:

curl --request POST \
 --url http://<keycloak-host>/auth/realms/<realm-name>/protocol/openid-connect/token \
 --header 'Content-Type: application/x-www-form-urlencoded' \
 --data 'grant_type=client_credentials' \
 --data 'client_id=<client-id>' \
 --data 'client_secret=<client-secret>'

Replace:

<keycloak-host>: The Keycloak server URL.
<realm-name>: The realm where your client is defined.
<client-id>: The client ID from Keycloak.
<client-secret>: The secret from the Keycloak admin panel.

This will return a response that includes an access token (JWT) in the form:
```
{
 "access_token": "eyJhbGciOiJSUzI1NiIs...",
 "expires_in": 300,
 "refresh_expires_in": 1800,
 ...
}
```
You can extract the access_token from the response, and use it to authenticate requests to your backend services.

4. Send the Token to Backend Services

Once you have the token, you can pass it to the backend service in the Authorization header as a Bearer token:

   curl --request GET \
     --url http://backend-service/api/endpoint \
     --header "Authorization: Bearer <access_token>"

5. Automate This in the Cron Job Container

In your cron job script, automate the process of:

Requesting the token from Keycloak using the client credentials flow.
Using the token to authenticate requests to your backend services.

Example Script for Cron Job

#!/bin/bash

# Step 1: Get JWT from Keycloak using client credentials flow
response=$(curl --silent --request POST \
  --url http://<keycloak-host>/auth/realms/<realm-name>/protocol/openid-connect/token \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --data 'grant_type=client_credentials' \
  --data 'client_id=<client-id>' \
  --data 'client_secret=<client-secret>')

# Step 2: Extract the access token from the response
access_token=$(echo $response | jq -r '.access_token')

# Step 3: Use the token to authenticate a request to backend service
curl --request GET \
  --url http://backend-service/api/endpoint \
  --header "Authorization: Bearer $access_token"

In this script:

The access_token is fetched from Keycloak and used to authenticate against the backend service.
jq is used to parse the JSON response to extract the token.

You can add this script to your Docker container and configure the cron job to execute it at scheduled intervals.

Summary

Keycloak Client Credentials Flow is used for non-interactive authentication (e.g., cron jobs).
The cron job requests a token from Keycloak, which it can then use to authenticate API requests to backend services.
Ensure the client in Keycloak has proper permissions and roles to access the necessary APIs.

spherulitic / xerafin3