<PackageReference Include="Microsoft.Identity.Client" Version="4.84.1" />

Microsoft.Identity.Client.ClientSignedAssertion

public class ClientSignedAssertion
Container returned from WithClientAssertion.
public string Assertion { get; set; }

Represents the client assertion (JWT) and optional mutual‑TLS binding certificate returned by the clientAssertionProvider callback supplied to WithClientAssertion.

Optional. Certificate used to bind the client assertion for mutual‑TLS Proof‑of‑Possession (PoP).