We created a simple iOS native app, which should allow users to login into SF once and then open Lightning community app in a Webview. For this purposes we have below steps:
1. User launch the mobile app;
2. App calls Mobile SDK, which redirects to community login page, where user enters login and password; That allows us to get and refresh session token if this is required.
3. We get an authorization token and passing community URL + token into WebView.
4. We tried to pass authorization token as a parameter like:

let request = try! URLRequest(url: URL(string: "<Link to community page>")!, method: .get, headers: ["Authorization" : "Bearer \(token!)"])
or using frontoor.jsp.

both ways works fine when I try to open classic SF page or application. But when I try to open Community page it asks login again. So that means that those ways does not work with a community pages.
So how can I pass authorization token to a Webview for a community users? Any help would be appreciated! Thanks!

Hi,
My name is Timur Khayaliev, I am Co-founder and head of Mobile practice department in JET BI company (http://jetbi.com).
Recently we founded Mobile department as a part of Salesforce department to develop lightweight and functional native apps based on Salesforce.
And now we are looking for a new projects.

We are young, but strong
Our department is young, but our team has experienced iOS and Android developers with strong Salesforce knowledges. 
Our main task for now -  to make a good portfolio and tell the world about yourself, that's why we are providing a really low prices and good service.

We will provide you

• Free statement of work and detailed estimates;
• Free prototype with Proof-of-Concept functionality;
• Free project manager who will be fully involved in the project;
• You will pay only when you are satisfied with the result!

We are using 

• InvisionApp;
• Jira;
• Google Enterprise;
• Diawi;
• Github;
• MVP;
• Agile Methodology.

Please do not hesitate to contact me.

Contacts:
e-mail: timur.khayaliev@jetbi.com
skype: robospot_

Best regards,
Timur Khayaliev