add PasswordAuthE func, which is like PasswordAuth but returns error instead of bool

example_test.go

@@ -1,6 +1,7 @@
 package ssh_test
 
 import (
+	"fmt"
 	"io"
 	"io/ioutil"
 
@@ -21,6 +22,17 @@ func ExamplePasswordAuth() {
 	)
 }
 
+func ExamplePasswordAuthE() {
+	ssh.ListenAndServe(":2222", nil,
+		ssh.PasswordAuthE(func(ctx ssh.Context, pass string) error {
+			if pass == "secret" {
+				return nil
+			}
+			return fmt.Errorf("password incorrect")
+		}),
+	)
+}
+
 func ExampleNoPty() {
 	ssh.ListenAndServe(":2222", nil, ssh.NoPty())
 }

options.go

@@ -14,6 +14,14 @@ func PasswordAuth(fn PasswordHandler) Option {
 	}
 }
 
+// PasswordAuthE returns a functional option that sets PasswordHandlerE on the server.
+func PasswordAuthE(fn PasswordHandlerE) Option {
+	return func(srv *Server) error {
+		srv.PasswordHandlerE = fn
+		return nil
+	}
+}
+
 // PublicKeyAuth returns a functional option that sets PublicKeyHandler on the server.
 func PublicKeyAuth(fn PublicKeyHandler) Option {
 	return func(srv *Server) error {

options_test.go

@@ -69,6 +69,57 @@ func TestPasswordAuthBadPass(t *testing.T) {
 	}
 }
 
+func TestPasswordAuthE(t *testing.T) {
+	t.Parallel()
+	testUser := "testuser"
+	testPass := "testpass"
+	session, _, cleanup := newTestSessionWithOptions(t, &Server{
+		Handler: func(s Session) {
+			// noop
+		},
+	}, &gossh.ClientConfig{
+		User: testUser,
+		Auth: []gossh.AuthMethod{
+			gossh.Password(testPass),
+		},
+		HostKeyCallback: gossh.InsecureIgnoreHostKey(),
+	}, PasswordAuthE(func(ctx Context, password string) error {
+		if ctx.User() != testUser {
+			t.Fatalf("user = %#v; want %#v", ctx.User(), testUser)
+		}
+		if password != testPass {
+			t.Fatalf("user = %#v; want %#v", password, testPass)
+		}
+		return nil
+	}))
+	defer cleanup()
+	if err := session.Run(""); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestPasswordAuthEBadPass(t *testing.T) {
+	t.Parallel()
+	l := newLocalListener()
+	srv := &Server{Handler: func(s Session) {}}
+	srv.SetOption(PasswordAuthE(func(ctx Context, password string) error {
+		return nil
+	}))
+	go srv.serveOnce(l)
+	_, err := gossh.Dial("tcp", l.Addr().String(), &gossh.ClientConfig{
+		User: "testuser",
+		Auth: []gossh.AuthMethod{
+			gossh.Password("testpass"),
+		},
+		HostKeyCallback: gossh.InsecureIgnoreHostKey(),
+	})
+	if err != nil {
+		if !strings.Contains(err.Error(), "unable to authenticate") {
+			t.Fatal(err)
+		}
+	}
+}
+
 type wrappedConn struct {
 	net.Conn
 	written int32

server.go

@@ -40,6 +40,7 @@ type Server struct {
 
 	KeyboardInteractiveHandler    KeyboardInteractiveHandler    // keyboard-interactive authentication handler
 	PasswordHandler               PasswordHandler               // password authentication handler
+	PasswordHandlerE              PasswordHandlerE              // password authentiication handler with error, if it is set, it overrides PasswordHandler
 	PublicKeyHandler              PublicKeyHandler              // public key authentication handler
 	PtyCallback                   PtyCallback                   // callback for allowing PTY sessions, allows all if nil
 	ConnCallback                  ConnCallback                  // optional callback for wrapping net.Conn before handling
@@ -126,7 +127,7 @@ func (srv *Server) config(ctx Context) *gossh.ServerConfig {
 	for _, signer := range srv.HostSigners {
 		config.AddHostKey(signer)
 	}
-	if srv.PasswordHandler == nil && srv.PublicKeyHandler == nil && srv.KeyboardInteractiveHandler == nil {
+	if srv.PasswordHandler == nil && srv.PasswordHandlerE == nil && srv.PublicKeyHandler == nil && srv.KeyboardInteractiveHandler == nil {
 		config.NoClientAuth = true
 	}
 	if srv.Version != "" {
@@ -141,6 +142,13 @@ func (srv *Server) config(ctx Context) *gossh.ServerConfig {
 			return ctx.Permissions().Permissions, nil
 		}
 	}
+	if srv.PasswordHandlerE != nil {
+		config.PasswordCallback = func(conn gossh.ConnMetadata, password []byte) (*gossh.Permissions, error) {
+			applyConnMetadata(ctx, conn)
+			err := srv.PasswordHandlerE(ctx, string(password))
+			return ctx.Permissions().Permissions, err
+		}
+	}
 	if srv.PublicKeyHandler != nil {
 		config.PublicKeyCallback = func(conn gossh.ConnMetadata, key gossh.PublicKey) (*gossh.Permissions, error) {
 			applyConnMetadata(ctx, conn)

ssh.go

@@ -41,6 +41,9 @@ type PublicKeyHandler func(ctx Context, key PublicKey) bool
 // PasswordHandler is a callback for performing password authentication.
 type PasswordHandler func(ctx Context, password string) bool
 
+// PasswordHandlerE is like PasswordHandler, but returns error
+type PasswordHandlerE func(ctx Context, password string) error
+
 // KeyboardInteractiveHandler is a callback for performing keyboard-interactive authentication.
 type KeyboardInteractiveHandler func(ctx Context, challenger gossh.KeyboardInteractiveChallenge) bool