Sample Authorization Function

// authorizeAPI/index.js

exports.handler = function(event, context, callback) {        
    console.log('Received event:', JSON.stringify(event, null, 2));

    var headers = event.headers;
    var resource = extractResource(event);
        
    // Perform authorization to return the Allow policy for correct parameters and 
    // the 'Unauthorized' error, otherwise.
    var authResponse = {};
    var condition = {};
    condition.IpAddress = {};
     
    if (headers.authtoken === "supersecretvalue" ) {
        callback(null, generateAllow('me', event.methodArn));
    }  else {
        callback("Unauthorized");
    }
}
     
// Helper function to generate an IAM policy
var generatePolicy = function(principalId, effect, resource) {
    // Required output:
    var authResponse = {};
    authResponse.principalId = principalId;
    if (effect && resource) {
        var policyDocument = {};
        policyDocument.Version = '2012-10-17'; // default version
        policyDocument.Statement = [];
        var statementOne = {};
        statementOne.Action = 'execute-api:Invoke'; // default action
        statementOne.Effect = effect;
        statementOne.Resource = resource;
        policyDocument.Statement[0] = statementOne;
        authResponse.policyDocument = policyDocument;
    }
    return authResponse;
}
     
var generateAllow = function(principalId, resource) {
    return generatePolicy(principalId, 'Allow', resource);
}
     
var generateDeny = function(principalId, resource) {
    return generatePolicy(principalId, 'Deny', resource);
}

var extractResource = function(event) {
    // Parse the input for the parameter values
    var tmp = event.methodArn.split(':');
    var apiGatewayArnTmp = tmp[5].split('/');
    var awsAccountId = tmp[4];
    var region = tmp[3];
    var restApiId = apiGatewayArnTmp[0];
    var stage = apiGatewayArnTmp[1];
    var method = apiGatewayArnTmp[2];
    var resource = '/'; // root resource
    if (apiGatewayArnTmp[3]) {
        resource += apiGatewayArnTmp[3];
    }

    return resource;
}