Refactor: Move login out of models (#16199)

`models` does far too much. In particular it handles all `UserSignin`.

It shouldn't be responsible for calling LDAP, SMTP or PAM for signing in.

Therefore we should move this code out of `models`.

This code has to depend on `models` - therefore it belongs in `services`.

There is a package in `services` called `auth` and clearly this functionality belongs in there.

Plan:

- [x] Change `auth.Auth` to `auth.Method` - as they represent methods of authentication.
- [x] Move `models.UserSignIn` into `auth`
- [x] Move `models.ExternalUserLogin`
- [x] Move most of the `LoginVia*` methods to `auth` or subpackages
- [x] Move Resynchronize functionality to `auth`
  - Involved some restructuring of `models/ssh_key.go` to reduce the size of this massive file and simplify its files.
- [x] Move the rest of the LDAP functionality in to the ldap subpackage
- [x] Re-factor the login sources to express an interfaces `auth.Source`?
  - I've done this through some smaller interfaces Authenticator and Synchronizable - which would allow us to extend things in future
- [x] Now LDAP is out of models - need to think about modules/auth/ldap and I think all of that functionality might just be moveable
- [x] Similarly a lot Oauth2 functionality need not be in models too and should be moved to services/auth/source/oauth2
  - [x] modules/auth/oauth2/oauth2.go uses xorm... This is naughty - probably need to move this into models.
  - [x] models/oauth2.go - mostly should be in modules/auth/oauth2 or services/auth/source/oauth2 
- [x] More simplifications of login_source.go may need to be done
- Allow wiring in of notify registration -  *this can now easily be done - but I think we should do it in another PR*  - see #16178 
- More refactors...?
  - OpenID should probably become an auth Method but I think that can be left for another PR
  - Methods should also probably be cleaned up  - again another PR I think.
  - SSPI still needs more refactors.* Rename auth.Auth auth.Method
* Restructure ssh_key.go

- move functions from models/user.go that relate to ssh_key to ssh_key
- split ssh_key.go to try create clearer function domains for allow for
future refactors here.

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/auth/source/smtp/assert_interface_test.go

@@ -0,0 +1,25 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package smtp_test
+
+import (
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/services/auth"
+	"code.gitea.io/gitea/services/auth/source/smtp"
+)
+
+// This test file exists to assert that our Source exposes the interfaces that we expect
+// It tightly binds the interfaces and implementation without breaking go import cycles
+
+type sourceInterface interface {
+	auth.PasswordAuthenticator
+	models.LoginConfig
+	models.SkipVerifiable
+	models.HasTLSer
+	models.UseTLSer
+	models.LoginSourceSettable
+}
+
+var _ (sourceInterface) = &smtp.Source{}

services/auth/source/smtp/auth.go

@@ -0,0 +1,81 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package smtp
+
+import (
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net/smtp"
+
+	"code.gitea.io/gitea/models"
+)
+
+//   _________   __________________________
+//  /   _____/  /     \__    ___/\______   \
+//  \_____  \  /  \ /  \|    |    |     ___/
+//  /        \/    Y    \    |    |    |
+// /_______  /\____|__  /____|    |____|
+//         \/         \/
+
+type loginAuthenticator struct {
+	username, password string
+}
+
+func (auth *loginAuthenticator) Start(server *smtp.ServerInfo) (string, []byte, error) {
+	return "LOGIN", []byte(auth.username), nil
+}
+
+func (auth *loginAuthenticator) Next(fromServer []byte, more bool) ([]byte, error) {
+	if more {
+		switch string(fromServer) {
+		case "Username:":
+			return []byte(auth.username), nil
+		case "Password:":
+			return []byte(auth.password), nil
+		}
+	}
+	return nil, nil
+}
+
+// SMTP authentication type names.
+const (
+	PlainAuthentication = "PLAIN"
+	LoginAuthentication = "LOGIN"
+)
+
+// Authenticators contains available SMTP authentication type names.
+var Authenticators = []string{PlainAuthentication, LoginAuthentication}
+
+// Authenticate performs an SMTP authentication.
+func Authenticate(a smtp.Auth, source *Source) error {
+	c, err := smtp.Dial(fmt.Sprintf("%s:%d", source.Host, source.Port))
+	if err != nil {
+		return err
+	}
+	defer c.Close()
+
+	if err = c.Hello("gogs"); err != nil {
+		return err
+	}
+
+	if source.TLS {
+		if ok, _ := c.Extension("STARTTLS"); ok {
+			if err = c.StartTLS(&tls.Config{
+				InsecureSkipVerify: source.SkipVerify,
+				ServerName:         source.Host,
+			}); err != nil {
+				return err
+			}
+		} else {
+			return errors.New("SMTP server unsupports TLS")
+		}
+	}
+
+	if ok, _ := c.Extension("AUTH"); ok {
+		return c.Auth(a)
+	}
+	return models.ErrUnsupportedLoginType
+}

services/auth/source/smtp/source.go

@@ -0,0 +1,66 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package smtp
+
+import (
+	"code.gitea.io/gitea/models"
+
+	jsoniter "github.com/json-iterator/go"
+)
+
+//   _________   __________________________
+//  /   _____/  /     \__    ___/\______   \
+//  \_____  \  /  \ /  \|    |    |     ___/
+//  /        \/    Y    \    |    |    |
+// /_______  /\____|__  /____|    |____|
+//         \/         \/
+
+// Source holds configuration for the SMTP login source.
+type Source struct {
+	Auth           string
+	Host           string
+	Port           int
+	AllowedDomains string `xorm:"TEXT"`
+	TLS            bool
+	SkipVerify     bool
+
+	// reference to the loginSource
+	loginSource *models.LoginSource
+}
+
+// FromDB fills up an SMTPConfig from serialized format.
+func (source *Source) FromDB(bs []byte) error {
+	return models.JSONUnmarshalHandleDoubleEncode(bs, &source)
+}
+
+// ToDB exports an SMTPConfig to a serialized format.
+func (source *Source) ToDB() ([]byte, error) {
+	json := jsoniter.ConfigCompatibleWithStandardLibrary
+	return json.Marshal(source)
+}
+
+// IsSkipVerify returns if SkipVerify is set
+func (source *Source) IsSkipVerify() bool {
+	return source.SkipVerify
+}
+
+// HasTLS returns true for SMTP
+func (source *Source) HasTLS() bool {
+	return true
+}
+
+// UseTLS returns if TLS is set
+func (source *Source) UseTLS() bool {
+	return source.TLS
+}
+
+// SetLoginSource sets the related LoginSource
+func (source *Source) SetLoginSource(loginSource *models.LoginSource) {
+	source.loginSource = loginSource
+}
+
+func init() {
+	models.RegisterLoginTypeConfig(models.LoginSMTP, &Source{})
+}

services/auth/source/smtp/source_authenticate.go

@@ -0,0 +1,71 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package smtp
+
+import (
+	"errors"
+	"net/smtp"
+	"net/textproto"
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/util"
+)
+
+// Authenticate queries if the provided login/password is authenticates against the SMTP server
+// Users will be autoregistered as required
+func (source *Source) Authenticate(user *models.User, login, password string) (*models.User, error) {
+	// Verify allowed domains.
+	if len(source.AllowedDomains) > 0 {
+		idx := strings.Index(login, "@")
+		if idx == -1 {
+			return nil, models.ErrUserNotExist{Name: login}
+		} else if !util.IsStringInSlice(login[idx+1:], strings.Split(source.AllowedDomains, ","), true) {
+			return nil, models.ErrUserNotExist{Name: login}
+		}
+	}
+
+	var auth smtp.Auth
+	if source.Auth == PlainAuthentication {
+		auth = smtp.PlainAuth("", login, password, source.Host)
+	} else if source.Auth == LoginAuthentication {
+		auth = &loginAuthenticator{login, password}
+	} else {
+		return nil, errors.New("Unsupported SMTP auth type")
+	}
+
+	if err := Authenticate(auth, source); err != nil {
+		// Check standard error format first,
+		// then fallback to worse case.
+		tperr, ok := err.(*textproto.Error)
+		if (ok && tperr.Code == 535) ||
+			strings.Contains(err.Error(), "Username and Password not accepted") {
+			return nil, models.ErrUserNotExist{Name: login}
+		}
+		return nil, err
+	}
+
+	if user != nil {
+		return user, nil
+	}
+
+	username := login
+	idx := strings.Index(login, "@")
+	if idx > -1 {
+		username = login[:idx]
+	}
+
+	user = &models.User{
+		LowerName:   strings.ToLower(username),
+		Name:        strings.ToLower(username),
+		Email:       login,
+		Passwd:      password,
+		LoginType:   models.LoginSMTP,
+		LoginSource: source.loginSource.ID,
+		LoginName:   login,
+		IsActive:    true,
+	}
+	return user, models.CreateUser(user)
+}