In the pre-carbon versions of WSO2 WSAS (2.* and older), you may have used WSAS_HOME/lib/extensions directory to put third party jars such as jdbc drivers.
After WSO2 WSAS became a part of WSO2 Carbon platform, a.k.a WSAS-3.* versions, all third party jars should be placed inside WSAS_HOME/repostiroy/components/lib directory of your WSAS distribution.
**This is applicable to all WSO2 Carbon products (WSAS, ESB, G-reg, IS, BPS)