fix: Prepend Docker Hub namespace to repository

[HofmeisterAn]

What does this PR do?

If the TESTCONTAINERS_HUB_IMAGE_NAME_PREFIX custom configuration contains a namespace, such as registry.example.com/library, Testcontainers retains the namespace when attempting to locate registry credentials. However, the registry credentials key does not (may not) include the namespace, preventing Testcontainers for .NET from finding and using existing credentials. This PR ensures that the namespace is prepended to the repository and that only the hostname is used to resolve registry credentials.

When we use the custom configuration from above, Testcontainers will resolve the following property values:

Property	Value
Registry	registry.example.com
Repository	library/testcontainers/helloworld
Tag	latest
GetHostname()	registry.example.com

Why is it important?

Fixes an issue where Testcontainers for .NET is unable to find existing and valid configured private registry credentials. This is a regression.

Related issues

• Closes [Bug]: Docker registry credential not found using TESTCONTAINERS_HUB_IMAGE_NAME_PREFIX (regression in 4.0.0) #1286

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[HofmeisterAn]

@kiview @mdelapenya, I need your guidance and expertise on how you handle this in other languages.

The Azure DevOps pipeline task Docker@2 (command: 'login') stores the Docker Registry credentials in Base64 in the config.json file. The pipeline task uses the exact Docker Registry value from the Azure DevOps service connection as key. E.g. for the Docker Registry value https://registry.example.com/library the JSON value will look like:

{"auths":{"https://registry.example.com/library":{"auth":"...","email":""}},"HttpHeaders":{"X-Meta-Source-Client":"VSTS"}}

The Base64Provider implementation does not expect a namespace (/library) segment. It only expects the Docker Registry hostname.

This results in that Testcontainers is unable to find matching credentials to authenticate against the Docker Registry. Right now, valid keys are:

• registry.example.com
• https://registry.example.com
• http://registry.example.com
• xyz://registry.example.com

However, the Docker CLI seams not that strict, it is still able to pull images with the configuration above.

As a workaround, users can change the Docker Registry service connection value to https://registry.example.com (remove the namespace segment). But this prevents users from configuring different credentials for different namespaces (not sure if that’s a use case; which this PR breaks already).