I can see you're having an issue with OAuth2 token introspection in your Oathkeeper setup. This is a common problem when running Ory services in Docker containers. The error message indicates that Oathkeeper is trying to connect to

localhost:4445

for token introspection instead of using the Docker container name

hydra:4445

. This happens because of how Docker networking and URL resolution works between containers. ## The Issue When configuring the OAuth2 introspection authenticator in Oathkeeper, you need to be careful about how URLs are resolved. The introspection URL needs to be resolvable from the Oathkeeper container, not from your host machine. ## Solution You should configure your Oathkeeper's

oauth2_introspection

authenticator with the proper introspection URL that uses the Docker container name:

yaml authenticators:   oauth2_introspection:     enabled: true     config:       introspection_url: <http://hydra:4445/oauth2/introspect>

This is because in Docker networking, container names can be used as hostnames within the same Docker network. ## Important Considerations 1. Administrative vs Public Endpoints: Remember that the introspection endpoint is part of Hydra's administrative API (port 4445), which should not be exposed to public internet traffic as mentioned in the [Hydra documentation](https://www.ory.sh/docs/hydra/self-hosted/production#exposing-administrative-and-public-api-endpoints). 2. Docker Network: Make sure both your Oathkeeper and Hydra containers are on the same Docker network. 3. URL Resolution: As seen in the [GitLab Hydra integration documentation](https://www.ory.sh/docs/hydra/self-hosted/gitlab#gitlab-configuration---oauth-2-setup), URLs are resolved differently depending on where they're being used: - URLs used in browser redirects need to be accessible from the user's browser - URLs for server-to-server communication (like introspection) need to use container names This issue is similar to one reported in [GitHub issue #3335](https://github.com/ory/hydra/issues/3335) where there were problems with URL resolution between containers. If you're still having issues after updating your configuration, you might want to check your Docker network setup and ensure that both containers can communicate with each other.

I see the issue now. Even though you've correctly configured

introspection_url: <http://hydra:4445/oauth2/introspect>

in your Oathkeeper configuration, it's still trying to connect to

localhost:4445

instead. This appears to be related to a known issue with URL handling in Oathkeeper. Looking at the knowledge sources, there are a couple of potential explanations: 1. Redirection issue: Based on [GitHub issue #3335](https://github.com/ory/hydra/issues/3335), there seems to be a problem where Hydra might be redirecting requests to localhost even when configured with a different host. The logs in that issue show:

http_response=map[headers:map[cache-control:private, no-cache, no-store, must-revalidate content-type:text/html; charset=utf-8 location:<http://localhost:4445/admin/clients]>

2. X-Forwarded headers issue: According to [GitHub issue #1139](https://github.com/ory/oathkeeper/issues/1139), Oathkeeper might not be properly handling X-Forwarded headers, which could affect how it resolves URLs. 3. Keto integration issue: There's also a similar issue mentioned in [GitHub issue #1220](https://github.com/ory/oathkeeper/issues/1220) where Oathkeeper is using an outdated endpoint format when connecting to Keto. ## Possible solutions: 1. Check your Docker network: Ensure both containers are on the same Docker network and can communicate with each other. 2. Try using the IP address: Instead of using the container name, try using the actual IP address of the Hydra container. 3. Check Hydra configuration: Make sure Hydra is properly configured to bind to the correct interface. As mentioned in the [Hydra documentation](https://www.ory.sh/docs/hydra/self-hosted/production#binding-to-different-interfaces-or-unix-sockets), you can use environment variables like

ADMIN_HOST

to specify the interface:

ADMIN_HOST=0.0.0.0

4. Inspect the request flow: Use tools like

tcpdump

or network inspection in Docker to see exactly what's happening with the requests. 5. Check for redirects: The error suggests that there might be a redirect happening. Make sure your Hydra configuration doesn't have any redirects set up that would change the hostname. If none of these solutions work, you might need to check if there's a version compatibility issue between your Oathkeeper and Hydra instances, as some of these issues have been fixed in newer versions. For more information on configuring OAuth2 introspection with Hydra, you can refer to the [Oathkeeper documentation on OAuth2 token introspection](https://www.ory.sh/docs/oathkeeper/oauth2-token-introspection-hydra). Let me know if any of these suggestions help resolve the issue! [Hydra Self-hosted Production](https://www.ory.sh/docs/hydra/self-hosted/production#exposing-administrative-and-public-api-endpoints) [GitHub issue #3335](https://github.com/ory/hydra/issues/3335) [GitHub issue #1139](https://github.com/ory/oathkeeper/issues/1139) [GitHub issue #1220](https://github.com/ory/oathkeeper/issues/1220) [Oathkeeper OAuth2 Token Introspection](https://www.ory.sh/docs/oathkeeper/oauth2-token-introspection-hydra)

I see the issue now. The error message

"http:///admin/oauth2/introspect": http: no Host in request URL"

is very revealing. Notice the triple slashes in the URL (

http:///admin/...

) - this indicates that there's no host specified in the URL that Hydra is trying to use. This matches exactly with an issue mentioned in the knowledge sources. In [GitHub issue #3335](https://github.com/ory/hydra/issues/3335), a user reported a similar problem where setting

SERVE_ADMIN_HOST

resulted in no host at all:

http_response=map[headers:map[...] location:http:///admin/oauth2/auth/requests/login?login_challenge=...] ...

The issue appears to be related to how Hydra handles the admin host configuration in version 2.x. When you set the admin host to

0.0.0.0

, Hydra is correctly binding to all interfaces, but it's not properly setting the host in the URLs it generates for redirects or internal requests. ## Possible solutions: 1. Set a specific hostname: Instead of using

0.0.0.0

, try setting the admin host to a specific hostname that can be resolved within your Docker network, such as the container name:

SERVE_ADMIN_HOST=hydra

2. Check your Hydra configuration: Make sure you have the correct configuration for URLs. In Hydra's configuration, there are separate settings for binding addresses and public-facing URLs:

yaml serve:   admin:     host: 0.0.0.0:4445  # This is for binding   admin_url: <http://hydra:4445/>  # This is for generating URLs

3. Use the latest versions: The issue might be fixed in newer versions. You're using Hydra 2.3.0, but there might be patches in newer releases that address this issue. 4. Network configuration: Ensure that your Docker network is properly configured and that the containers can resolve each other's names. This appears to be a known issue with Hydra's URL handling when configured with certain host settings. The problem is that Hydra is generating URLs without a proper host when redirecting or handling internal requests. [GitHub issue #3335](https://github.com/ory/hydra/issues/3335) mentions this exact problem, and it seems to be related to how Hydra handles the admin host configuration in version 2.x. Let me know if any of these suggestions help resolve your issue!

Based on the error you're experiencing with the OAuth2 token introspection, I can see that your Hydra configuration needs some adjustments. The issue is that when you set

host: 0.0.0.0

, Hydra is binding to all interfaces but not properly setting the host in the URLs it generates, resulting in the

http:///admin/oauth2/introspect

error (notice the missing host). Here's what you should change in your Hydra configuration:

yaml serve:   cookies:     same_site_mode: Lax   admin:     host: 0.0.0.0     # Add this section to specify the public-facing URL     url: <http://hydra:4445/>

The key addition here is the

url

parameter under

admin

. This tells Hydra what URL to use when generating links for the admin API, which is critical for the introspection endpoint to work correctly. This solution is based on the issue described in [GitHub issue #3335](https://github.com/ory/hydra/issues/3335), where a similar problem was reported with URLs missing the host component. If you're using environment variables instead of a YAML file, you would set:

SERVE_ADMIN_HOST=0.0.0.0 SERVE_ADMIN_URL=<http://hydra:4445/>

Make sure both your Oathkeeper and Hydra containers are on the same Docker network so that the hostname

hydra

can be properly resolved from the Oathkeeper container. Let me know if this resolves your issue!

I see you're still having issues with the OAuth2 token introspection despite having the correct configuration and confirming network connectivity between your containers. Looking at your configuration:

- SERVE_ADMIN_HOST=0.0.0.0 - SERVE_ADMIN_URL=<http://hydra:4445/> oauth2_introspection:     enabled: true     config:       introspection_url: <http://hydra:4445/oauth2/introspect>

And you've confirmed connectivity with:

docker exec -it oathkeeper wget -O- <http://hydra:4445/health/ready>

Since the health endpoint works but the introspection doesn't, let's look at some specific issues that might be causing this problem: ## Possible issues to check: 1. Introspection endpoint path: According to the [Hydra API Reference](https://www.ory.sh/docs/hydra/reference/api), the correct introspection endpoint is actually:

POST /admin/oauth2/introspect

So your introspection URL should be:

introspection_url: <http://hydra:4445/admin/oauth2/introspect>

2. Token format: Make sure you're sending the token correctly in the request body. According to the documentation, it should be sent as form data with the key

token

. 3. Headers: Check if you need to add any specific headers to the introspection request. The Oathkeeper configuration allows for

introspection_request_headers

to be specified. 4. Hydra version compatibility: You mentioned you're using Hydra 2.3.0 and Oathkeeper 0.40.9. There might be compatibility issues between these versions. Try updating your Oathkeeper configuration to use the correct introspection endpoint path:

yaml oauth2_introspection:   enabled: true   config:     introspection_url: <http://hydra:4445/admin/oauth2/introspect>

If that doesn't work, you might want to try using the Hydra CLI to manually test the introspection endpoint to see if it's working correctly:

docker exec -it hydra hydra introspect token YOUR_TOKEN --endpoint <http://hydra:4445>

This would help determine if the issue is with the Hydra configuration or with how Oathkeeper is making the request. Let me know if changing the introspection URL path helps resolve the issue! [Hydra API Reference](https://www.ory.sh/docs/hydra/reference/api)