Extract data that Jenkins receives from POST hooks sent by eg. github or bitbucket

Try using Apache as a proxy in front of Jenkins. I Use NameVirtualHost...

<VirtualHost>
  --Snip---    

<Proxy *>
      AddDefaultCharSet Off
      Order deny,allow
      Allow from all
     --snip-- #You can tighten this to only allow from GITHUB ips.
</Proxy>

    RequestHeader unset Authorization
    RequestHeader set Authorization "Basic [AUTHSTRING]"
    ProxyPass / [AJP|HTTP]://[JENKINS]:[PORT]/
    ProxyPassReverse / [AJP|HTTP]://[JENKINS]:[PORT]/

</VirtualHost>

I run Jenkins in a tomcat container and use AJP, so the var [AJP|HTTP] can be either for the proxy. The [JENKINS] and [PORT] variables should be intuitive.

Now the hard part, [AUTHSTRING]!

Take the USERNAME:PASSWORD part and run it through this command:

$ echo -n 'username:password' | base64
 dXNlcm5hbWU6cGFzc3dvcmQ=

(echo -n is important to remove the newline.) Take the result and put in [AUTHSTRING]

You should be able to remove the user:password from the line at github.

For my build (on a Linux host), I do something like this (as a build step in Jenkins) to execute a build script out of the freshly-checked-out workspace:

Execute shell Command:

 sh -x $WORKSPACE/build/myproject.build

I presume it would work similar on Windows, except of course you would use \ rather than / and you're using python rather than sh to execute your script.