How to read Sharepoint Online sites sharing capabilities via CSOM

Sharepoint Online allows to share your sites with external users. At first administrator should enable external sharing on the tenant (organization) level (see Manage sharing settings). After that you may set external capabilities for each individual site (see Set sharing capabilities of Sharepoint site collection via client object model for how to do that). In provided example SharingCapabilities is enum which has the following values (they are quite self-descriptive so I won’t describe they here):

• Disabled
• ExternalUserSharingOnly
• ExternalUserAndGuestSharing
• ExistingExternalUserSharingOnly

In order to read sharing capabilities of existing Sharepoint Online sites via CSOM you may use the following example:

string username = ...;
string password = ...;
var adminContext = new ClientContext("https://{tenant}-admin.sharepoint.com");
var secure = new SecureString();
foreach (char c in password)
{
    secure.AppendChar(c);
}
var credentials = new SharePointOnlineCredentials(username, secure);
adminContext.Credentials = credentials;
adminContext.Load(adminContext.Site);
adminContext.ExecuteQuery();

var tenant = new Tenant(adminContext);
var properties = tenant.GetSiteProperties(0, true);
adminContext.Load(properties);
adminContext.ExecuteQuery();
foreach (SiteProperties p in properties)
{
    Console.WriteLine(p.Url + ": " + p.SharingCapability);
}

This example outputs all sites with their SharingCapability properties. If you need to get SharingCapability for single specific site add condition on site url to the last loop. Hope it will help you.