[AI Gateway] Rename injected transformer provider parameter to provider-id

[Aakashwije]

Purpose

The OpenAI multi-provider transformer policies now use provider-id as the injected parameter identifying their target upstream provider. The Gateway Controller previously injected this value using params["id"], creating a contract mismatch that could prevent transformer policies from selecting and routing to the correct upstream.

This change aligns the Gateway Controller with the transformer policy contract.

Related changes:

• [Transformers] Add OpenAI multi-provider transformer policies gateway-controllers#222
• [Transformer] add Bedrock transformer gateway-controllers#228

Goals

• Inject the provider upstream name using the provider-id parameter.
• Keep provider selection and upstream routing consistent across all transformer policies.
• Preserve the existing resolution behavior where additionalProviders[].as is used when configured, otherwise falling back to additionalProviders[].id.
• Update tests and samples to reflect the renamed parameter.

Approach

The Gateway Controller’s multi-provider transformer construction has been updated to inject:

params["provider-id"] = name

The existing provider-name resolution remains unchanged:

• Use additionalProviders[].as when configured.
• Otherwise, use additionalProviders[].id.

The corresponding unit-test assertion and multi-provider proxy sample documentation were updated to use provider-id.

This change does not affect the UI.

User stories

• As an API developer, I want multi-provider transformer policies to receive the expected provider identifier so requests are routed to the correct upstream provider.
• As a platform developer, I want the Gateway Controller and transformer policies to use a consistent parameter contract.
• As an operator, I want existing additionalProviders[].id and additionalProviders[].as configurations to continue working without changes.

Documentation

No product documentation impact. The parameter is injected internally by the Gateway Controller and is not manually configured when a transformer is attached to an additional provider.

The openai-multi-provider-proxy.yaml sample comments were updated to document the internal provider-id contract.

Automation tests

• Unit tests

  • Updated TestLLMProviderTransformer_TransformProxy_AdditionalProviderTransformerIsConditional to verify that the resolved provider upstream name is injected through params["provider-id"].
  • The focused Gateway Controller unit test passes.
  • Code coverage was not measured separately for this focused change.

• Integration tests

  • No new integration tests were added.
  • The change is limited to renaming an internally injected transformer parameter.
  • Existing provider selection, execution conditions, and upstream-name resolution remain unchanged.

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? Yes
• Ran FindSecurityBugs plugin and verified report? N/A — this is a Go change; FindSecurityBugs is a Java/SpotBugs plugin
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? Yes

Samples

Updated the OpenAI multi-provider proxy sample comments to explain that each transformer receives its resolved upstream provider name through provider-id.

No sample configuration fields were renamed:

• additionalProviders[].id remains unchanged.
• additionalProviders[].as remains unchanged.
• Router mappings and selected_provider metadata remain unchanged.

Related PRs

• [Transformers] Add OpenAI multi-provider transformer policies gateway-controllers#222
• [Transformer] add Bedrock transformer gateway-controllers#228
• [AI Gateway] Add multi-provider routing for LLM proxies #2586

Test environment

• Go: 1.26.x
• Operating system: macOS, ARM64
• JDK: N/A
• Database: N/A
• Browser: N/A

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