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>

models/migrations/v189_test.go

@@ -0,0 +1,83 @@
+// 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 migrations
+
+import (
+	"testing"
+
+	jsoniter "github.com/json-iterator/go"
+	"github.com/stretchr/testify/assert"
+)
+
+// LoginSource represents an external way for authorizing users.
+type LoginSourceOriginalV189 struct {
+	ID        int64 `xorm:"pk autoincr"`
+	Type      int
+	IsActived bool   `xorm:"INDEX NOT NULL DEFAULT false"`
+	Cfg       string `xorm:"TEXT"`
+	Expected  string `xorm:"TEXT"`
+}
+
+func (ls *LoginSourceOriginalV189) TableName() string {
+	return "login_source"
+}
+
+func Test_unwrapLDAPSourceCfg(t *testing.T) {
+
+	// Prepare and load the testing database
+	x, deferable := prepareTestEnv(t, 0, new(LoginSourceOriginalV189))
+	if x == nil || t.Failed() {
+		defer deferable()
+		return
+	}
+	defer deferable()
+
+	// LoginSource represents an external way for authorizing users.
+	type LoginSource struct {
+		ID       int64 `xorm:"pk autoincr"`
+		Type     int
+		IsActive bool   `xorm:"INDEX NOT NULL DEFAULT false"`
+		Cfg      string `xorm:"TEXT"`
+		Expected string `xorm:"TEXT"`
+	}
+
+	// Run the migration
+	if err := unwrapLDAPSourceCfg(x); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+
+	const batchSize = 100
+	for start := 0; ; start += batchSize {
+		sources := make([]*LoginSource, 0, batchSize)
+		if err := x.Table("login_source").Limit(batchSize, start).Find(&sources); err != nil {
+			assert.NoError(t, err)
+			return
+		}
+
+		if len(sources) == 0 {
+			break
+		}
+
+		for _, source := range sources {
+			converted := map[string]interface{}{}
+			expected := map[string]interface{}{}
+
+			if err := jsoniter.Unmarshal([]byte(source.Cfg), &converted); err != nil {
+				assert.NoError(t, err)
+				return
+			}
+
+			if err := jsoniter.Unmarshal([]byte(source.Expected), &expected); err != nil {
+				assert.NoError(t, err)
+				return
+			}
+
+			assert.EqualValues(t, expected, converted, "unwrapLDAPSourceCfg failed for %d", source.ID)
+			assert.EqualValues(t, source.ID%2 == 0, source.IsActive, "unwrapLDAPSourceCfg failed for %d", source.ID)
+		}
+	}
+
+}