fix: extend forgejo_auth_token table

- Add a `purpose` column, this allows the `forgejo_auth_token` table to
be used by other parts of Forgejo, while still enjoying the
no-compromise architecture.
- Remove the 'roll your own crypto' time limited code functions and
migrate them to the `forgejo_auth_token` table. This migration ensures
generated codes can only be used for their purpose and ensure they are
invalidated after their usage by deleting it from the database, this
also should help making auditing of the security code easier, as we're
no longer trying to stuff a lot of data into a HMAC construction.
-Helper functions are rewritten to ensure a safe-by-design approach to
these tokens.
- Add the `forgejo_auth_token` to dbconsistency doctor and add it to the
`deleteUser` function.
- TODO: Add cron job to delete expired authorization tokens.
- Unit and integration tests added.

(cherry picked from commit 1ce33aa38d)

v7: Removed migration - XORM can handle this case automatically without migration.

assert.Equal(t, `doesnotexist@example.com`, msgs[0].To) in tests
because v7 does not include the user name to the recipient.

models/auth/auth_token.go

@@ -15,12 +15,31 @@ import (
 	"code.gitea.io/gitea/modules/util"
 )
 
+type AuthorizationPurpose string
+
+var (
+	// Used to store long term authorization tokens.
+	LongTermAuthorization AuthorizationPurpose = "long_term_authorization"
+
+	// Used to activate a user account.
+	UserActivation AuthorizationPurpose = "user_activation"
+
+	// Used to reset the password.
+	PasswordReset AuthorizationPurpose = "password_reset"
+)
+
+// Used to activate the specified email address for a user.
+func EmailActivation(email string) AuthorizationPurpose {
+	return AuthorizationPurpose("email_activation:" + email)
+}
+
 // AuthorizationToken represents a authorization token to a user.
 type AuthorizationToken struct {
 	ID              int64  `xorm:"pk autoincr"`
 	UID             int64  `xorm:"INDEX"`
 	LookupKey       string `xorm:"INDEX UNIQUE"`
 	HashedValidator string
+	Purpose         AuthorizationPurpose `xorm:"NOT NULL DEFAULT 'long_term_authorization'"`
 	Expiry          timeutil.TimeStamp
 }
 
@@ -41,7 +60,7 @@ func (authToken *AuthorizationToken) IsExpired() bool {
 // GenerateAuthToken generates a new authentication token for the given user.
 // It returns the lookup key and validator values that should be passed to the
 // user via a long-term cookie.
-func GenerateAuthToken(ctx context.Context, userID int64, expiry timeutil.TimeStamp) (lookupKey, validator string, err error) {
+func GenerateAuthToken(ctx context.Context, userID int64, expiry timeutil.TimeStamp, purpose AuthorizationPurpose) (lookupKey, validator string, err error) {
 	// Request 64 random bytes. The first 32 bytes will be used for the lookupKey
 	// and the other 32 bytes will be used for the validator.
 	rBytes, err := util.CryptoRandomBytes(64)
@@ -56,14 +75,15 @@ func GenerateAuthToken(ctx context.Context, userID int64, expiry timeutil.TimeSt
 		Expiry:          expiry,
 		LookupKey:       lookupKey,
 		HashedValidator: HashValidator(rBytes[32:]),
+		Purpose:         purpose,
 	})
 	return lookupKey, validator, err
 }
 
 // FindAuthToken will find a authorization token via the lookup key.
-func FindAuthToken(ctx context.Context, lookupKey string) (*AuthorizationToken, error) {
+func FindAuthToken(ctx context.Context, lookupKey string, purpose AuthorizationPurpose) (*AuthorizationToken, error) {
 	var authToken AuthorizationToken
-	has, err := db.GetEngine(ctx).Where("lookup_key = ?", lookupKey).Get(&authToken)
+	has, err := db.GetEngine(ctx).Where("lookup_key = ? AND purpose = ?", lookupKey, purpose).Get(&authToken)
 	if err != nil {
 		return nil, err
 	} else if !has {