Implementation of OAUTHBEARER/OIDC metadata based authentication

[emasab]

initially supporting the Azure UAMI method.

[confluent-cla-assistant]

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[Copilot]

Pull Request Overview

This PR implements OAUTHBEARER/OIDC metadata-based authentication, initially supporting the Azure UAMI (User Assigned Managed Identity) method for token retrieval.

• Adds Azure UAMI metadata authentication support for OAUTHBEARER/OIDC
• Refactors HTTP client to support custom headers and retry logic
• Introduces configuration parameter for metadata authentication type

Reviewed Changes

Copilot reviewed 13 out of 16 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/rdkafka_sasl_oauthbearer_oidc.c	Implements Azure metadata token refresh callback with HTTP calls to Azure UAMI endpoint
src/rdkafka_sasl_oauthbearer_oidc.h	Declares the new Azure metadata token refresh callback function
src/rdkafka_conf.h	Adds metadata authentication type enum and configuration structure
src/rdkafka_conf.c	Adds configuration property and refactors OIDC validation logic into separate functions
src/rdkafka_sasl_oauthbearer.c	Simplifies builtin token refresh callback detection logic
src/rdkafka.c	Integrates Azure metadata authentication into the OIDC token refresh mechanism
src/rdhttp.h	Updates HTTP client interface to support headers, timeouts, and retries
src/rdhttp.c	Enhances HTTP client with parameter appending, custom headers, and retry functionality
CONFIGURATION.md	Documents the new metadata authentication type configuration parameter
tests/0126-oauthbearer_oidc.c	Removes duplicate configuration line in test

[Copilot]

Assigning '\0' (character literal) to a const char* pointer is incorrect. This should be NULL for an empty/null pointer, or "" for an empty string.

Suggested change

	.params = '\0';
	.params = NULL;

[Copilot]

This condition appears to check if the insertion position is before the question mark, but the logic seems inverted. If we're inserting before a question mark, we likely shouldn't skip it.

Suggested change

	if (has_question_mark && (url + insert_pos) < has_question_mark)
	if (has_question_mark && (url + insert_pos) > has_question_mark)

[emasab]

No, this the case where the question mark is inside the hash instead of before it

[Copilot]

The memory allocation doesn't account for the remaining part of the URL after the insertion point (hash fragment). This will truncate the URL if there's a hash fragment.

Suggested change

	of += params_len;
	/* Calculate length of the remainder of the URL after the insertion point */
	size_t remainder_len = strlen(url + insert_pos);
	ret = rd_malloc(insert_pos + strlen(separator) + params_len + remainder_len + 1);
	memcpy(ret, url, insert_pos);
	of += insert_pos;
	if (separator[0]) {
	ret[of] = separator[0];
	of++;
	}
	memcpy(ret + of, params, params_len);
	of += params_len;
	/* Copy the remainder of the URL (e.g., hash fragment) */
	memcpy(ret + of, url + insert_pos, remainder_len);
	of += remainder_len;

[emasab]

hash fragment needs to be removed

[Copilot]

The function doesn't copy the remaining part of the original URL after the insertion point (such as hash fragments). This will result in truncated URLs.

Suggested change

	of += params_len;
	/* Calculate length of the remaining part of the URL (e.g., hash fragment) */
	size_t remaining_len = strlen(url + insert_pos);
	ret = rd_malloc(insert_pos + strlen(separator) + params_len + remaining_len + 1);
	memcpy(ret, url, insert_pos);
	of += insert_pos;
	if (separator[0]) {
	ret[of] = separator[0];
	of++;
	}
	memcpy(ret + of, params, params_len);
	of += params_len;
	/* Copy the remaining part of the URL (e.g., hash fragment) */
	memcpy(ret + of, url + insert_pos, remaining_len);
	of += remaining_len;

[emasab]

hash fragment needs to be removed

[Copilot]

[nitpick] The headers_array is defined as a local variable but could be a const static array since it never changes, improving performance and memory usage.

Suggested change

	char *headers_array[] = {"Metadata: true"};
	static const char *headers_array[] = {"Metadata: true"};