It limits current to protect the switch (transistor, etc.) and allows signal sources with limited driving capability to change that node's voltage. Rails generally have high drive capability, or low resistance. Think voltage divider, including source impedance of signal and rail, then let the rail impedance be 0-ohms for simplicity.

Other factors, other than operating current and voltage drops, to determine the pull resistance is charge time and substrate leakage. A 2M-ohm pull-down resistor on a top layer exposed to humidity and salts won't do anything due to sub-1M-ohm electrical resistance of grime layer.

Why the use of resistors when pulling something up or down?
I'm currently implementing a Spring MVC application that is both an OAuth client (in the sense that it consumes data from third party service providers), and an OAuth2 Service Provider (in the sense that it should provide the means for third party oauth clients to consume data from this application from a dedicated REST api). 

While I have no issue with the implementation of the application in its capacity as OAuth client, my OAuth2 service provider configuration is interfering with the applications ability to authenticate with service providers- if I enable the Oauth2 config, it appears to intercept callbacks to the application from third party service providers. Disabling it returns the application back to its normal working state.

I'm assuming that this is because I am not specifying which urls I want to the oauth2 provider to govern exclusively- but I can't see any way of specifying this. 

To simplify the question how do I configure Spring Security OAuth2 provider to manage one url root (e.g. '/restapi/*'), and this url only, with it ignoring all other urls entirely? I've had a look at the resources at the projects homepage, but nothing is jumping out at me... 

This may well be down to how I've defined my security intercept-urls, in which case it may not be an OAuth2 specific question, but how to apply different security schemes to different url schemes. Any advice on how to do that would be great!
