How to deal with external libraries when developing IoT Gateway Interceptor?

I am currently developing an IoT Gateway Interceptor using some external libraries such as libraries related to org.apache.http.client.*. When testing the interceptor on my local machine in eclipse without the gateway, everything works as planned, but when executed as an OSGi bundle within the Gateway, only the InterceptorActivator starts up but no message of the actual interceptor is found in the log. There are just dozens of error messages in the error log in folder "configuration" of the type "java.lang.NoClassDefFoundError: org/apache/http/client/ [...]".

I figure that somehow the included libraries went missing when building the OSGi bundle / when clicking "Build Iot Interceptor in Eclipse.

Thanks in advance for your help!