Queries the service provider for an access token.
Pre-conditions: the given {@link OAuthConsumer} must have a validconsumer key, consumer secret, authorized request token and token secret already set.
Post-conditions: the given {@link OAuthConsumer} will have anaccess token and token secret set.
@param consumer the {@link OAuthConsumer} that should be used to sign the request
@param oauthVerifier
NOTE: Only applies to service providers implementing OAuth 1.0a. Set to null if the service provider is still using OAuth 1.0. The verification code issued by the service provider after the the user has granted the consumer authorization. If the callback method provided in the previous step was {@link OAuth.OUT_OF_BAND}, then you must ask the user for this value. If your app has received a callback, the verfication code was passed as part of that request instead.
@param customOAuthParams you can pass custom OAuth parameters here which will go directly into the signer, i.e. you don't have to put them into the request first. This is useful for pre-setting OAuth params for signing. Pass them sequentially in key/value order.
@throws OAuthMessageSignerException if signing the request failed
@throws OAuthNotAuthorizedException if the service provider rejected the consumer
@throws OAuthExpectationFailedException if required parameters were not correctly set by the consumer or service provider
@throws OAuthCommunicationException if server communication failed