CredentialsContainer.store()

CredentialsContainer.store(Credential).then(function(Credential) { ... } )

// Check if the browser supports password credentials (and the Credential Management API)
if ("PasswordCredential" in window) {
  let credential = new PasswordCredential({
    id: "example-username",
    name: "John Doe", // In case of a login, the name comes from the server.
    password: "correct horse battery staple"
  });

  navigator.credentials.store(credential).then(() => {
    console.info("Credential stored in the user agent's credential manager.");
  }, (err) => {
    console.error("Error while storing the credential: ", err);
  });
}