Enforce dedicated service account for Cloud Build triggers

[alex-doudou]

• Tests pass
• Appropriate changes to documentation are included in the PR

This PR:

• updated how_to_create_cloudbuild_trigger.md to include a mandatory step for creating/using a dedicated service account.
• explicitly assigned required roles (logging, artifactregistry, developerconnect) to the dedicated SA.
• mandated passing the dedicated SA email to the create_build_trigger tool.

[gemini-code-assist]

Summary of Changes

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This pull request enhances the security posture for Cloud Build triggers by mandating the use of dedicated service accounts. It ensures that triggers operate with the principle of least privilege, thereby reducing potential security risks. The changes primarily involve updating documentation to guide users through the process of setting up and assigning appropriate roles to these dedicated service accounts, and explicitly requiring their use when creating new triggers.

Highlights

• Mandatory Dedicated Service Accounts: Enforced the use of dedicated, user-managed service accounts for Cloud Build triggers to adhere to the principle of least privilege, replacing the default Compute Engine service account.
• Required IAM Roles: Explicitly defined the minimum necessary IAM roles (roles/logging.logWriter, roles/artifactregistry.writer, roles/developerconnect.tokenAccessor) that must be granted to the dedicated service account.
• Tool Parameter Update: Mandated that the email of the dedicated service account must be provided to the service_account parameter when using the create_build_trigger tool.
• Documentation Update: Updated the how_to_create_cloudbuild_trigger.md guide to include detailed steps for checking, creating, and configuring the dedicated service account.

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[gemini-code-assist]

Code Review

This pull request updates the how_to_create_cloudbuild_trigger.md documentation to include a new section on ensuring a dedicated service account is used for Cloud Build triggers, detailing the creation process and required roles, and emphasizes providing this service account to the create_build_trigger tool. Feedback indicates a critical discrepancy where the create_build_trigger tool does not enforce the use of a dedicated service account, potentially leading to security issues, and suggests modifying the tool to require this parameter. Additionally, a minor markdown formatting issue was noted in a new heading.

[gemini-code-assist]

This documentation mandates the use of a dedicated service account, which is an important security best practice. However, the implementation of the create_build_trigger tool (in cicd-mcp-server/cloudbuild/cloudbuild.go) doesn't enforce this. The service_account parameter is optional, and if omitted, the tool silently falls back to the default Compute Engine service account. This creates a significant discrepancy between the documentation's requirement and the tool's behavior, potentially leading to the use of an over-privileged service account. To align with the goal of this PR, the create_build_trigger tool should be modified to require the service_account parameter.

[alex-doudou]

Addressed in the follow-up commit. (will squash after human review is approved)

[gemini-code-assist]

The markdown for this heading, ### ###, is not standard and will likely not render as intended. For a level 3 heading, a single ### should be used.

Suggested change

	### ### 4. Ensure Dedicated Service Account Exists
	### 4. Ensure Dedicated Service Account Exists

[alex-doudou]

Resolved

[alex-doudou]

Added the follow up commit to enforce the service account behaviour in our go tool as well.

The commit:

• Modified create_build_trigger to require the service_account parameter.
• Removed silent fallback to the default Compute Engine service account.
• Updated unit tests to verify the mandatory behavior and removed obsolete fallback tests.