An authentication method should be selected for a use case based on the auth method that best establishes the identity of the client. The identity of the client is the basis for assigning a set of policies and permissions to the client in Vault. Different auth methods have different ways of verifying the identity of the client, such as using passwords, tokens, certificates, cloud credentials, etc. Depending on the use case, some auth methods may be more suitable or convenient than others. For example, for human users, the userpass or ldap auth methods may be easy to use, while for machines or applications, the approle or aws auth methods may be more secure and scalable. The choice of the auth method should also consider the trade-offs between security, performance, and usability. References: Auth Methods | Vault | HashiCorp Developer, Authentication - Concepts | Vault | HashiCorp Developer