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Is it safe to use php proxy to do https request in javascript?

As you know you can not make http requests to sites that do not have the http header that allows it using JavaScript in browsers because of CORS. I need to make https requests containing sensitive data. I do not want to get in touch with this sensitive data, in fact all this will be client side with javascript, only for the reason mentioned above I need to use a php proxy such as CORS Anywhere or my own, the question is: if I use these proxies to make https requests directly to the direct interested server, will the proxy have any information regarding the data sent? Sorry for my bad english, I use the translator.

Javascript API hindered by Cross Domain API calls

I need to provide a functionality similar to "Share with Facebook" for my social networking site. Facebook uses nested iframes and also xd_receiver concepts. I want to write a JavaScript API(JS file hosted on my domain), which can be used by different sites to call my web server APIs in order to share, post or recommend on my social networking site. I have a few questions -
Even though I provide the JS API, and diff sites load the JS file using the source, if any API call is made, it will again be a cross domain call(If I am comprehending correctly) and will be rejected on the server?
How to overcome such situation?
Is there any other better mechanism to implement this functionality?
Please suggest so that I can proceed with the implementation.

I think the default way is to use jsonp to get around cross domain limitation. http://en.wikipedia.org/wiki/JSONP. It might require a change in your api though. A user requests your api through the src of a script tag passing in a function callback. Your api would return pass your json response to the function specified.

Do you know why they use iframes and not simple get requests with JSONP/Images/scripts?
The answer is security. I cannot write a script that clicks their button which will automatically "like" the page.
Using plain old JavaScript with a JSONP will allow the developer to automatically click the button. Do you want that to happen?

The requests are made by the browser and not from the JS file, so, your requests will be cross-domain every time they did from another domain site.
Your server will only reject cross-domain requests if you implement a referrer validation.
And you can use JSONP if your API needs custom contents from your site...

To allow cross domain requests, you need to set the following Header in your HTTP Response:
Access-Control-Allow-Origin: *
The implementation will vary depending on the back-end you are using.
If the host in the Origin header of the request is anything but the host of the request, the response must include the listed Origin in the Access-Control-Allow-Origin header. Setting this header to * will allow all origins.
For very specific information on cross origin resource sharing see http://www.w3.org/TR/cors/. If you're not big on reading w3c documents, check out MDN's primer.
Note: Internet Explorer does its own thing with regards to cross domain requests. This answer is a good start if you have issues with IE.

AJAX and server security using http access-control-allow-*

I'm working on a JavaScript library and I would like anybody using it can make request to my server.
Because this I have added the access-control-allow-origin,method headers to my server responses.
Thigs works fine but my is question is: Is that secure for my server? there is any other implication I can take into account?
Thanks a lot.

It's as secure as the code on your server is. If you allow people to send an AJAX request that can drop a table, then no it's not secure. But if you follow best practices for website/scripting security it should be as safe as handling any other request your server normally would.

Can anonymous users make changes to your server (e.g. incrementing a vote counter, post a comment, delete a post, etc)? If so, does it matter if a website you don't control makes some or all of their users make use of this feature of your site? Do the access control headers allow remote XHR to make those requests? If so, you have a problem.
Can known users make changes to your server? If so, does it matter if a website you don't control makes some or all of their users who are also your users make use of this feature of your site? Do the access control headers allow remote XHR to make those requests? Do the access control headers allow authentication methods (such as cookies) through? If so, you have a problem.
In short:
Can a user do something potentially undesirable on your site?
Do your access-control headers prevent third party websites from making users do those undesirable things?

javascript / ajax question

I'm wondering if anyone knows a javascript library where I could remotely login to a site, then browse pages upon logging in.
This is very easy with php's curl but I'm wondering if there is a javascript equivalent where I can execute multiple remote url's under a single http session.
Basically what I'm looking to do is post a username/password to one of my sites and then immediately post some other commands to a different url (same remote domain) using the authenticated session.
I haven't come across anything like this yet so I'm wondering if anyone can point me in the direction (if it's even possible). Can definitely be HTML5.

Due to same origin policy restrictions in browsers this is not possible using javascript. You need a server side script that will act as a bridge between your site and the remote sites. Then talk to this local script using AJAX.

There are some techniques available to bypass the same origin policy:
If you don't need to read the response of your POST calls, you can create a FORM by javascript with an action to any url (not limited to the same origin policy) like in this question: How do I send a cross-domain POST request via JavaScript?
But this means you rely only on session cookies for the security, this is open for XSS attacks.
As you own the other domain site, you could develop a small service that returns a JSON with the data you need, and use the JSONP technique, eg:
<script src="http://otherdomain/curl?url=page.html&callback=cb">
</script>
May be you could signin before using the POST technique above and sending a secret token that you reuse in the url to improve the security.
And finally there is a way to act/read on other pages using a bookmarklet.The idea is to inject in the other domain's page a script that can run with all the privileges, and send back information to your domain.
But this requires a manual action (click a link or a browser bookmark)

How can i get around the same origin policy?

I need to use AJAX to get the content of another page located on a different server from the one the AJAX is loaded from. The AJAX needs to send a POST request then return the result. how can i do this?

Set up proxy on your own server. Have your server call theirs and return the result.

if you control both servers, you can use one of the HTTP header fields for cross-origin resource sharing:
http://www.petefreitag.com/item/703.cfm
https://developer.mozilla.org/En/HTTP_access_control

There is no way to go around that policy. This policy is there for very good reasons.
That is also no problem as long as you're in control over the web application. You could simply redirect the call to the other server from your webserver and pass the result. This would work out like a proxy.

If you want to do that on the client and cross browser, you need some cooperation from the other server.
Either by:
1) using JSONP (inject a script tag with a callback function)
Only GET calls are possible though.
Security is an issue as the script has access to all resources in that page(data, cookies, ...).Here's a post that explain how to sandbox them and keep the data in your page safe.
2) POST looks possible using Kris Zip's window.name technique
If the cooperation from the other server is impossible, the server proxy as described in other answers is, to my knowledge, the only option left.