Some APIs that use this module allow the developer to pass the same querystring parameter multiple times. For instance, see SimpleGeo and categories... https://simplegeo.com/docs/api-endpoints/simplegeo-places

The oauth implementation turns querystring parameters into object, so a given parameter can only exist one time, so it changes the parameter name to be category[0], categort[1], etc.

I devised a way to fix this by modifying "exports.OAuth.prototype._normaliseRequestParams" to look like this...

exports.OAuth.prototype._normaliseRequestParams= function(arguments) {
var argument_pairs= this._makeArrayOfArgumentsHash(arguments);

// David DeRemer: added logic to allow for multiple occurrences of the same querystring parameter
for (var i=0; i<argument_pairs.length; i++) {
if (argument_pairs[i][0].search(/[\d_]/) != -1) {
argument_pairs[i] = [argument_pairs[i][0].replace(/[\d_]/,''), argument_pairs[i][1]];
}
}

// First encode them #3.4.1.3.2 .1
for(var i=0;i<argument_pairs.length;i++) {
argument_pairs[i][0]= this._encodeData( argument_pairs[i][0] );
argument_pairs[i][1]= this._encodeData( argument_pairs[i][1] );
}

// Then sort them #3.4.1.3.2 .2
argument_pairs= this._sortRequestParams( argument_pairs );

// Then concatenate together #3.4.1.3.2 .3 & .4
var args= "";
for(var i=0;i<argument_pairs.length;i++) {
args+= argument_pairs[i][0];
args+= "="
args+= argument_pairs[i][1];
if( i < argument_pairs.length-1 ) args+= "&";
}
return args;
}

You may want to consider adding something like this into the main branch.