source: code/trunk/vendor/github.com/emersion/go-sasl/login.go@ 822

package sasl

import (
        "bytes"
)

// The LOGIN mechanism name.
const Login = "LOGIN"

var expectedChallenge = []byte("Password:")

type loginClient struct {
        Username string
        Password string
}

func (a *loginClient) Start() (mech string, ir []byte, err error) {
        mech = "LOGIN"
        ir = []byte(a.Username)
        return
}

func (a *loginClient) Next(challenge []byte) (response []byte, err error) {
        if bytes.Compare(challenge, expectedChallenge) != 0 {
                return nil, ErrUnexpectedServerChallenge
        } else {
                return []byte(a.Password), nil
        }
}

// A client implementation of the LOGIN authentication mechanism for SMTP,
// as described in http://www.iana.org/go/draft-murchison-sasl-login
//
// It is considered obsolete, and should not be used when other mechanisms are
// available. For plaintext password authentication use PLAIN mechanism.
func NewLoginClient(username, password string) Client {
        return &loginClient{username, password}
}

// Authenticates users with an username and a password.
type LoginAuthenticator func(username, password string) error

type loginState int

const (
        loginNotStarted loginState = iota
        loginWaitingUsername
        loginWaitingPassword
)

type loginServer struct {
        state              loginState
        username, password string
        authenticate       LoginAuthenticator
}

// A server implementation of the LOGIN authentication mechanism, as described
// in https://tools.ietf.org/html/draft-murchison-sasl-login-00.
//
// LOGIN is obsolete and should only be enabled for legacy clients that cannot
// be updated to use PLAIN.
func NewLoginServer(authenticator LoginAuthenticator) Server {
        return &loginServer{authenticate: authenticator}
}

func (a *loginServer) Next(response []byte) (challenge []byte, done bool, err error) {
        switch a.state {
        case loginNotStarted:
                // Check for initial response field, as per RFC4422 section 3
                if response == nil {
                        challenge = []byte("Username:")
                        break
                }
                a.state++
                fallthrough
        case loginWaitingUsername:
                a.username = string(response)
                challenge = []byte("Password:")
        case loginWaitingPassword:
                a.password = string(response)
                err = a.authenticate(a.username, a.password)
                done = true
        default:
                err = ErrUnexpectedClientResponse
        }

        a.state++
        return
}