background.js

chrome.cookies.onChanged.addListener(function(ci){
	if(ci.cookie.name=="oauth_code"&&ci.cookie.domain=="accounts.google.com"&&ci.cookie.path=="/o/oauth2/programmatic_auth"&&ci.removed==false){
		chrome.extension.sendMessage(null,{oauth:ci.cookie.value});
	}
});

content.js

sr = function(obj) {
  var str = [];
  for(var p in obj){
  	str.push(encodeURIComponent(p) + "=" + encodeURIComponent(obj[p]).replace('*','%2A'));
  }
  return str.join("&");
}

login_error = function(){
	$('.bar').parent().addClass('progress-danger');
	$('#proc').text($('#proc').text()+' 失败！');
}

$(function(){
	client_secret='q-tA1vMJhkoeoucVH7NfvryX';
	client_id='545553600905.apps.googleusercontent.com';
	$('#submit').click(function(e){
		chrome.runtime.getBackgroundPage(function(){});
		chrome.tabs.create({
			"url":'https://accounts.google.com/o/oauth2/programmatic_auth?client_id=545553600905.apps.googleusercontent.com&scope=https%3A%2F%2Fwww.google.com%2Faccounts%2FOAuthLogin%20https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fuserinfo.email'
		},function(tab){
			chrome.extension.onMessage.addListener(function(message, sender, sendResponse) {
				if(typeof message.oauth =='undefined'){
					return;
				}
				chrome.tabs.remove(tab.id);
				$("#procModal").modal();
				$('#proc').text('正在验证 - 第1步');
				$.ajax({
					url:'https://accounts.google.com/o/oauth2/token',
					processData:false,
					type:'POST',
					dataType:'json',
					error:login_error,
					data:sr({
						client_id:client_id,
						client_secret:client_secret,
						code:message.oauth,
						grant_type:"authorization_code",
						scope:'https://www.google.com/accounts/OAuthLogin https://www.googleapis.com/auth/userinfo.email'
					}),
					success:function(data,stat){
						if(typeof data.access_token != 'undefined'){
							$('.bar').css('width','20%');
							$('#proc').text('正在验证 - 第2步');
							var refresh_token=data.refresh_token;
							var auth=data.token_type+' '+data.access_token;
							$.ajax({
								url:"https://www.googleapis.com/oauth2/v1/userinfo",
								headers:{'Authorization':auth},
								type:'GET',
								dataType:'json',
								error:login_error,
								success:function(data,stat){
									if(typeof data.id !='undefined'){
										userinfo=data;
										$('.bar').css('width','40%');
										$('#proc').text('正在验证 - 第3步');
										$.ajax({
											url:'https://accounts.google.com/o/oauth2/token',
											processData:false,
											type:'POST',
											dataType:'json',
											error:login_error,
											data:sr({
												client_id:client_id,
												client_secret:client_secret,
												grant_type:'refresh_token',
												refresh_token:refresh_token
											}),
											success:function(data,stat){
												if(typeof data.access_token != 'undefined'){
													$('.bar').css('width','60%');
													$('#proc').text('正在验证 - 第4步');
													auth=data.token_type+' '+data.access_token;
													$.ajax({
														url:'https://www.googleapis.com/oauth2/v2/IssueToken',
														processData:false,
														headers:{'Authorization':auth},
														type:'POST',
														dataType:'json',
														error:login_error,
														data:sr({
															app_id:'com.google.GooglePlus.*',
															client_id:client_id,
															client_secret:client_secret,
															response_type:'code',
															hl:'zh-Hans',
															scope:"https://www.googleapis.com/auth/plus.me https://www.googleapis.com/auth/plus.stream.read https://www.googleapis.com/auth/plus.stream.write https://www.googleapis.com/auth/plus.circles.write https://www.googleapis.com/auth/plus.circles.read https://www.googleapis.com/auth/plus.photos.readwrite https://www.googleapis.com/auth/plus.native"
														}),
														success:function(data,stat){
															if(typeof data.code !='undefined'){
																$('.bar').css('width','80%');
																$('#proc').text('正在验证 - 第5步');
																$.ajax({
																	url:'https://accounts.google.com/o/oauth2/token',
																	processData:false,
																	type:'POST',
																	dataType:'json',
																	error:login_error,
																	data:sr({
																		client_id:client_id,
																		client_secret:client_secret,
																		code:data.code,
																		grant_type:"authorization_code",
																		redirect_uri:'urn:ietf:wg:oauth:2.0:oob'
																	}),
																	success:function(data,stat){
																		if(typeof data.access_token != 'undefined'){
																			$('.bar').css('width','100%').parent().addClass('progress-success');
																			$('#proc').text('验证成功，正在处理');
																			console.log(data);
																		}else{login_error();}
																	}
																});
															}else{login_error();}
														}
													});
												}else{login_error();}
											}
										});
									}else{login_error();}
								}
							});
						}else{login_error();}
					}
				});
			});
		});
	});

});

manifest.json

{
  "manifest_version": 2,

  "name": "Google Plus Plus Login Helper",
  "version": "1.0",
  "background": { "scripts": ["background.js"],"persistent": false},
  "permissions": [
    "cookies",
    "*://*.google.com/",
    "*://*.googleapis.com/",
    "tabs",
    "storage"
  ],
  "options_page":"opt.html"
}

opt.html

<html>
	<head>
		<title>Google++ Backup Helper</title>
		<script type="text/javascript" src="jquery.min.js"></script>
		<script type="text/javascript" src="/bootstrap/js/bootstrap.min.js"></script>
		<link rel="stylesheet" href="/bootstrap/css/bootstrap.css">
		<script type="text/javascript" src="content.js"></script>
	</head>
	<body>
		<div class="well">
			<button id="submit" class="btn btn-large btn-primary">Google账号授权</button>
			<span class="help-inline">使用OAuth方式登录，请确认您已登录Google+。</span>
		</div>
		<div class="modal hide fade" id="procModal">
			<div class="modal-header">
    			<button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
    			<h3 id="ModalLabel">正在处理</h3>
  			</div>
  			<div class="modal-body">
  				<span class="help-block" id='proc'>正在授权，这可能需要一点时间。</span>
  				<div class="progress progress-striped active">
  					<div class="bar" style="width: 0%;"></div>
				</div>
  			</div>
		</div>
	</body>
</html>