Spring AI 2 regression authentication to Azure Open AI with custom Credential Builder

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Bug description

Switching from Spring Ai 1 to Spring AI 2.0.1 removes UAMI authentication for Azure Foundry models.

See https://github.com/spring-projects/spring-ai/blob/bf122ac7f92b805dd3391387004788456c5c03c6/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/setup/OpenAiSetup.java#L191

->

https://github.com/spring-projects/spring-ai/blob/bf122ac7f92b805dd3391387004788456c5c03c6/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/setup/AzureInternalOpenAiHelper.java#L51

	static Credential getAzureCredential() {
		return getAzureCredential(new DefaultAzureCredentialBuilder().build());
	}

There is no way to override that.

Environment
Spring AI 2.0.1, Java 25

Steps to reproduce
Authenticate against Azure OpenAI with Managed Identity

Expected Behavior

Spring AI 2 supports authentication to Azure Open AI with custom credential builder (UAMI, AASP)

Current Behavior

Spring AI 2 supports only API Key Based auth authentication OR AZURE_CLIENT_ID - single env variable, which limits our multi model configuration.

Start with models/spring-ai-openai/src/main/java/org/springframework/ai/openai/setup/OpenAiSetup.java around line 191 and AzureInternalOpenAiHelper.java around line 51. Trace how Azure credentials are selected and compare the Spring AI 1 to 2.0.1 behavior. Done means custom credential-builder authentication works for managed identity and multi-model configuration without relying only on an API key or AZURE_CLIENT_ID.