OAuth2 is a security protocol that allows Salesforce users to access their data without having to enter their username and password into an untrusted application or deal with nefarious token management.
A guide on how to install OAuth2 for web sites is available from Salesforce. If you've never worked with OAuth2, it can be tough to get started, but there are lots of resources accessible.
I would also recommend testing the use of OAuth2 with something like Firefox's RESTClient plugin (or something similar) to get a feel for authenticating against Salesforce.
Hope this helps!
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