Make CLIENT_SECRET optional

* Forcing CLIENT_SECRET to be mandatory restricted implementations that
wanted to use unauthorized clients.
* Example issue:
bshaffer/oauth2-server-php#644

README.md

@@ -73,7 +73,7 @@ Tables
 | Field         | Type             | Null | Key | Default | Extra |
 +---------------+------------------+------+-----+---------+-------+
 | client_id     | varchar(80)      | NO   | PRI | NULL    |       |
-| client_secret | varchar(80)      | NO   |     | NULL    |       |
+| client_secret | varchar(80)      | YES  |     | NULL    |       |
 | redirect_uri  | varchar(2000)    | YES  |     | NULL    |       |
 | grant_types   | varchar(80)      | YES  |     | NULL    |       |
 | scope         | varchar(4000)    | YES  |     | NULL    |       |

oauth.ddl

@@ -58,7 +58,7 @@ CREATE TABLE oauth_authorization_codes (
 
 CREATE TABLE oauth_clients (
   client_id            VARCHAR(80)   NOT NULL COMMENT 'Unique client identifier',
-  client_secret        VARCHAR(80)   NOT NULL COMMENT 'Client secret',
+  client_secret        VARCHAR(80)            COMMENT 'Client secret',
   redirect_uri         VARCHAR(2000)          COMMENT 'Redirect URI used for Authorization Grant',
   grant_types          VARCHAR(80)            COMMENT 'Space-delimited list of grant types permitted, null = all',
   scope                VARCHAR(4000)          COMMENT 'Space-delimited list of approved scopes',