According to the AWS Cloud Operations and Identity Management documentation, when configuring federation between IAM Identity Center (formerly AWS SSO) and an external SAML 2.0 identity provider, two key prerequisites are required:

The IAM Identity Center SAML metadata file — This is uploaded to the external IdP to establish trust, define SAML endpoints, and enable identity federation.

The IdP metadata (including the public X.509 certificate) — This information is imported into IAM Identity Center to validate authentication assertions and encryption signatures.

IAM Identity Center and the IdP exchange this metadata to mutually establish secure, bidirectional federation.

Network-level details such as IP addresses (Option C) are unnecessary. Root access (Option D) or permissions to member accounts (Option E) are not required; only Control Tower or IAM administrative permissions in the management account are needed for setup.

Thus, the correct answer is A and B — the SAML metadata from both sides is required for federation.