The authentication methods / construct / protocol validates the identity of a user (ie validates who you are).
The method is implemented by a (identify|authentication) provider.
Username / Password
In the traditional client-server authentication model, the third-party application requests an access-restricted resource (protected resource) on the server by authenticating with the server using the resource owner's credentials (generally a username/password). The resource owner shares then its credentials with the third party app.
|What is and how works the Basic Authentication scheme? (HTTP)
|Authentication - HTTP Digest Access Authentication
The cleartext protocols should be used together with HTTPS to encrypt the credentials in transit.
An Identity assertion Authentication use as credentials:
Strong authentication are generally based on identity_assertion