add setHeaders option

README.md

@@ -100,6 +100,8 @@ The following options are recognized by both methods:
   Example: `['Origin', 'X-Requested-With']`.
 * array of lowercase strings `removeHeaders` - Exclude certain headers from being included in the request.  
   Example: `["cookie"]`
+* dictionary of lowercase strings `setHeaders` - Set headers for the request (overwrites existing ones).  
+  Example: `{"x-powered-by": "CORS Anywhere"}`
 
 `createServer` recognizes the following option as well:
 

lib/cors-anywhere.js

@@ -200,7 +200,8 @@ var getHandler = exports.getHandler = function(options, proxy) {
     originBlacklist: [],      // Requests from these origins will be blocked.
     originWhitelist: [],      // If non-empty, requests not from an origin in this list will be blocked.
     requireHeader: null,      // Require a header to be set?
-    removeHeaders: []         // Strip these request headers
+    removeHeaders: [],        // Strip these request headers.
+    setHeaders: []            // Set these request headers.
   };
   if (options) {
     Object.keys(corsAnywhere).forEach(function(option) {
@@ -293,6 +294,9 @@ var getHandler = exports.getHandler = function(options, proxy) {
       delete req.headers[header];
     });
 
+    Object.keys(corsAnywhere.setHeaders).forEach(function(header) {
+      req.headers[header] = corsAnywhere.setHeaders[header];
+    });
 
     req.corsAnywhereRequestState = {
       location: location,

test/test.js

@@ -478,6 +478,26 @@ describe('removeHeaders', function() {
   });
 });
 
+describe('setHeaders', function() {
+  before(function() {
+    cors_anywhere = createServer({
+      setHeaders: {'x-powered-by': 'CORS Anywhere'},
+    });
+    cors_anywhere_port = cors_anywhere.listen(0).address().port;
+  });
+  after(stopServer);
+
+  it('GET /example.com', function(done) {
+    request(cors_anywhere)
+      .get('/example.com/echoheaders')
+      .expect('Access-Control-Allow-Origin', '*')
+      .expectJSON({
+        host: 'example.com',
+        'x-powered-by': 'CORS Anywhere'
+      }, done);
+  });
+});
+
 describe('httpProxyOptions.xfwd=false', function() {
   before(function() {
     cors_anywhere = createServer({