The problem requires granting an external partner team access solely to a database, without extending to other network resources, and following Google-recommended practices.

Workforce Identity Federation: This Google Cloud IAM feature is specifically designed for scenarios where an organization needs to grant Google Cloud access to external identities (like partners, contractors, or customers) who are managed by their own identity provider (IdP). It allows these external users to authenticate using their existing credentials and then gain access to specified Google Cloud resources.

Extract Reference: "Workforce Identity Federation lets you use an external identity provider (IdP) to authenticate and authorize a workforce—a group of users, such as employees, partners, and contractors—using IAM, so that the users can access Google Cloud services." (Google Cloud Documentation: "Workforce Identity Federation | IAM Documentation" - https://cloud.google.com/iam/docs/workforce-identity-federation)

Extract Reference: "Secure access for partners and vendors. Workforce Identity Federation can enable enterprises to selectively federate users from partner or vendor IdPs without requiring IT teams to sync or create a separate identity store to use Google Cloud resources." (Google Cloud Documentation: "Introducing Workforce Identity Federation..." - https://www.azalio.io/introducing-workforce-identity-federation-to-easily-manage-workforce-access-to-google-cloud/)

Least Privilege and Isolation: With Workforce Identity Federation, you create an identity pool and a provider that trusts the partner's IdP. You then grant IAM roles only to the workforce pool (or specific identities within it) on the specific database resource. This ensures fine-grained access control and prevents access to other resources in your network, directly addressing the least privilege and isolation requirements. The partner's identities are never synced into your internal Cloud Identity directory.

Let's evaluate the other options:

A. Add a public IP address... Securely distribute credentials: Adding a public IP address exposes the database to the internet, which is a major security risk and contradicts "restricted solely to the database and can not extend to any other resources within your company's network" as it allows any external network to potentially reach it. Distributing credentials manually is also not a Google-recommended secure practice.

B. Create accounts for the partner team in your corporate identity provider. Synchronize these accounts with Google Cloud Identity: This means you become responsible for managing the partner's identities within your own corporate IdP and syncing them. This is an unnecessary operational burden and blurs the lines of identity management. It also may inadvertently grant them broader network access if your corporate IdP is connected to your internal network resources.

C. Ask the partner team to set up Cloud Identity accounts within their own corporate environment and identity provider. Grant the partner’s Cloud Identity accounts access: While better than B, this implies the partner managing Cloud Identity accounts themselves and you directly granting IAM roles to their Cloud Identity users. Workforce Identity Federation is a more robust and scalable solution for federating any external IdP with Google Cloud IAM, rather than requiring partners to adopt Cloud Identity directly. Workforce Identity Federation is the explicit pattern for cross-organization access using existing external IdPs.

Therefore, Workforce Identity Federation is the most secure, scalable, and Google-recommended solution for granting restricted access to external partner teams.