code: func (c *CredentialsClient) SSHAgentLogin(ctx context.Context, user string, password string, otpToken string, pubKey []byte, ttl time.Duration, compatibility string) (*auth.SSHLoginResponse, error) {
  	re, err := c.clt.PostJSON(ctx, c.clt.Endpoint("webapi", "ssh", "certs"), CreateSSHCertReq{
  		User:          user,
  		Password:      password,
  		OTPToken:      otpToken,
  		PubKey:        pubKey,
  		TTL:           ttl,
  		Compatibility: compatibility,
  	})
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	var out *auth.SSHLoginResponse
  	err = json.Unmarshal(re.Bytes(), &out)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	return out, nil
  }
docs: // SSHAgentLogin is used by tsh to fetch local user credentials.