MySql : Grant privileges for specific session
Another approach is to provide a general read-only user and publicize the password.

To create the hundred GRANTS, 

SELECT  CONCAT("GRANT SELECT   ON ",
                schema_name, ".* TO 'read_only_user'@'*'
                IDENTIFIED BY 'foo'"
              )
    FROM  `SCHEMATA`
    WHERE  schema_name NOT IN ('information_schema', 'mysql',
                               'performance_schema');


(Then copy &amp; paste the results into the mysql commandline tool.)  (Or make a Stored Procedure to do the work.)