func (a Auth) AsMechanism() sasl.Mechanism {
	return Plain(func(context.Context) (Auth, error) {
		return a, nil
	})
}
AsMechanism returns a sasl mechanism that will use 'a' as credentials for
all sasl sessions.

This is a shortcut for using the Plain function and is useful when you do
not need to live-rotate credentials.
package plain
import (
	"context"
	"errors"
	"github.com/twmb/franz-go/pkg/sasl"
)
type Auth struct {
	Zid string
	User string
	Pass string
	_internal struct{}  
}