Accessing Sharepoint Web Services without authentication - sharepoint

Is it possible to access a sharepoint web service without authenication? If you can't do it directley can you think of any ways to get round it such as haveing an open service inbetween that does authenicate for you using a public account.

John,
The security model of the web application through which you're trying to access the web service in question is going to drive whether or not you can access the service anonymously. If you're attempting to access the web service through a web application on which anonymous access is enabled, then you'll be able to hit the web service. Go ahead and try this on an anonymous site (if you have one): http://yoursitehere/_vti_bin/lists.asmx. You'll get the friendly service page back, no auth required.
Here's the catch: once you traverse the web service layer, you've got another layer of security to deal with. SharePoint itself is going to want to check permissions for access via the web services just as it normally would, so unless you are attempting an operation or trying to access data that is allowed for anonymous users, you're going to get blocked.
You have a handful of options:
Simply ensure that everything you're trying to do is permitted anonymously. This may sound easy, but it can actually be pretty difficult for anything but the simplest and straightforward of operations. Most organizations, too, don't care for opening things up to this extent.
If you control the code that's calling the web service, then you have the ability to attach credentials to the web service request. I recommend starting here, as it is going to make things a lot easier than trying to throw everything wide open. Plenty of examples exist on attaching credentials to a web service proxy (e.g., http://msdn.microsoft.com/en-us/security/cc178918.aspx)
Finally, you could write your own web service that wraps the SharePoint web service (or services) of interest. You could permit anonymous access to your web service and then adopt an appropriate security context within your own service to access SharePoint with the required permissions level.
I hope this helps!
Sean

I don't think you can, most actions the webservices perform need an explicit user with the correct permissions set. If both sites are internal, your options might include
Using automatic NTLM authentication, give the complete Authenticated Users group the necessary acecss. Using IE or the proper extensions to FireFox credentials will be automatically passed without user prompting. Your mileage may vary.
Passing the proper credentials to a default user explicitly in the call to the webservice
from that other website.
If you feel creative, here is a blog from Reza Alirezaei where he walks through the steps of mapping the anonymous user onto a specific account. If you manage to give that acount the proper permissions, you are there. Not for the faint of heart, though.

Related

Open Azure App Service Endpoint to Only a Few Applications

I've implemented an ASP.NET Web API app as an Azure App Service. It has an App Registration, everything works as expected. I can hit the API from a browser and see all the JSON it returns. Now what I want to do is ensure that nothing except one or more applications from a set list can actually get anything from this endpoint. The applications needing access will all be custom ones in my organization/tenant. With all the flexibility and options, I'm having a very hard time determining what I need to do to lock the API down in this way.
I was envisioning having some client secrets the API knows about, and let the authorized applications supply them. Other methods would certainly be acceptable.
I'm certain this must be a duplicate question, but due to the plethora of information out there, and the myriad techniques for running applications on Azure, I can't seem to find just the right solution for my simple case.
It sounds like you have implemented interactive browser redirect-based authentication on the API.
Instead, you should implement JWT authentication on the API.
Then in Azure AD you can define permissions that can be granted to client applications.
In that way you can control which app can do what.
https://joonasw.net/view/azure-ad-authentication-aspnet-core-api-part-1
https://joonasw.net/view/azure-ad-authentication-aspnet-core-api-part-2
https://learn.microsoft.com/en-us/azure/active-directory/develop/scenario-protected-web-api-overview
https://learn.microsoft.com/en-us/azure/active-directory/develop/v2-permissions-and-consent

Multi Instance Apps and Azure Authentication Best Practices

We have a multi-instance Saas Application:
Each of our clients is given their own instance and their own subdomain for the site.
Our application (Web app & API) is protected by Azure, currently with the ADAL javascript libraries
We also have a second API for system-level integration that needs to be protected, currently using a second 'native' azure app, but this is likely incorrect and we want to consolidate
Our application reads and writes to the Azure AD both through the AzureAD Graph API and Microsoft Graph API (including password reset calls)
We're looking at Azure AD application configuration options and want to make sure we're building the most sensible and secure Azure AD Application. Here are some of the documentation we've been looking at:
https://learn.microsoft.com/en-us/azure/active-directory/develop/active-directory-integrating-applications
https://learn.microsoft.com/en-us/azure/active-directory/develop/active-directory-v2-protocols-oauth-client-creds
https://learn.microsoft.com/en-us/azure/architecture/multitenant-identity/
https://learn.microsoft.com/en-us/azure/active-directory/develop/active-directory-v2-compare
We want the application to be multi-tenant to ease configuration, and allow availability in the Gallery; but when looking into doing so we're left with some security questions.
A. Which application version to use
1) v1. Allows access to both Graph API. And as suggested by Microsoft we should use this when we're not concerned with Microsoft Accounts.
2) v2. When looking at the MS Graph API documentation it recommends using v2. Reportedly doesn't work for AzureAD Graph API? Allows the same app to be of multiple types (Web App/API and native), which we may or may not need to protect both our web api and our system api (which we're still trying to model).
B. How to manage the reply URL when our clients have different sub-domains?
I've noted the following options:
1) On the app registry, we add the reply urls for all of our customers. This seems okay because we only need to do it once, but feels odd. Is there a limit to the number of reply urls?
2) Have one reply url, but manage an external tool to route the responses to the correct instance, leveraging the state url parameter. Microsoft seems to be suggesting that in this link: https://learn.microsoft.com/en-us/azure/architecture/multitenant-identity/authenticate I'm not sure if ADAL allows us to set the state for a return subdomain url though. Is this approach common?
3) Is it possible for each ServiceProvider instance in our client's directories to configure the reply url to their own subdomain? I feel like this would be the cleanest approach, but I don't see documentation for it. It would be nice if we could set the replyURL programmatically as well.
C. How to manage authorization to the Graph APIs (AzureAD and Microsoft Graph)
I've noted the following options:
1) Use the client credential flow, with a single application key (used for all clients). As clients subscribe they will admin consent with our app to give the application permission to their directory. Of course we'd do our best to keep that key secure. But if for some reason it was compromised this would put all of our clients at risk, not just the one instance that was compromised.
2) Same as 1, but use a certificate instead of a secret key. I understand this could be a little more secure, but I don't see how it wouldn't suffer from the same issue as 1.
3) Instead of using application permissions, use delegated permissions with an admin user. This would be good, in that it inherently prevents one instance of our app from talking to the wrong directory. However changes to the administrator may interrupt service; and I think it is best audit-wise that our application is responsible for the changes it makes. (Also, do delegated permissions allow for password resetting? I know for app permissions you need to run powershell script to upgrade the application's directory role)
4) Is there some way for the service principal to generate a unique key for it's directory on creation? can this be handed back to our app programmatically? Perhaps during admin consent?
Really good questions. I'll try to answer each to the best of my knowledge, but if someone has other ideas, feel free to comment/add your own answer.
A. Which application version to use
v2 should allow you to call Azure AD Graph API. The documentation you linked shows an example of specifying Azure AD Graph scopes:
GET https://login.microsoftonline.com/common/oauth2/v2.0/authorize?client_id=2d4d11a2-f814-46a7-890a-274a72a7309e&scope=https%3A%2F%2Fgraph.windows.net%2Fdirectory.read%20https%3A%2F2Fgraph.windows.net%2Fdirectory.write
The main decision point if you should use v2 is: Do you need to support Microsoft accounts which are not in an Azure AD? If yes, you need to use v2. Otherwise there is no problem using v1 (well, lack of dynamic permissions).
Since you are using Azure AD Graph to modify things, I'm going to guess pure Microsoft accounts will not work for you. I would recommend sticking with v1.
v2 also has some limits: https://learn.microsoft.com/en-us/azure/active-directory/develop/active-directory-v2-limitations
B. How to manage the reply URL when our clients have different sub-domains?
I could not find documentation on a limit for URLs. It could be that you can add however many you want. But I am not sure :)
If your subdomains look like this: https://customer.product.com, you can configure the reply URL as:
https://*.product.com
It will then allow any subdomain to be specified in the redirect_uri.
Though note that at the time of writing this, wildcard reply URLs are not supported in v2.
C. How to manage authorization to the Graph APIs (AzureAD and Microsoft Graph)
Using multiple keys makes no sense as they are all equal anyway :) Any of them could be used to call another tenant.
You can store the secret/certificate in an Azure Key Vault, and then use Azure AD Managed Service Identity to get it on app startup.
I would prefer using delegated permissions, but if the users of the app won't have the rights to do the things your app needs to do then that does not work.
I would just make sure it is not possible for a customer's instance to call to the APIs with another tenant id. And also make sure token caches are separated in such a way that it is not possible to get another tenant's access token (an in-memory cache on the instance would be good).

Can ASP.NET Web API treat security differently when request comes from inside the firewall?

I'm new to Web API, HTTP and security in general, but I just want to know if this is possible: for a controller to relax security requirements when the HTTP request originated from within the local area network.
My particular application has very low security requirements for clients inside the firewall. For instance, I want internal client apps to be able to make requests of controller actions marked with [AllowAnonymous] so that they don't need to deal with OAuth, etc (which just seems like complete overkill for my internal use scenario).
However, if the same controller actions are available to the public Internet, of course strict security requirements should apply.
Can security be handled differently based on origin? Or is the standard practice to expose both a public-facing and an Internal API?
When you use the [AllowAnonymous] attribute on your controller or action, you tell ASP.NET that it should not check the user's identity at all. That is not what you want for users coming from the internet.
You could remove the [Authorize] attribute from your controller and manually check inside the action if the user is authenticated using:
if (User.Identity.IsAuthenticated || IsLocalUser())
{
// action implementation
}
You can implement this check in a custom authorization attribute.
This still leaves you with the task to determine whether the user is local or coming from the internet. You could check the client IP-address to determine this of course.
Another option would be to enable both Windows authentication and bearer scheme authentication if your local users are part of an Active Directory domain.
Users from your intranet could use Windows authentication to talk to the service, while internet users need to bring a JWT token. This would only work if the client application for users coming from the internet is different than for local users.
DISCLAIMER: I've never tried this last option.
Identifying a request as one from "inside the firewall" isn't always as simple as just investigating the IP address. Although, this may work for you now, it may make it difficult to move environments or modify the environment without affecting application logic.
I would recommend developing a simple middle layer application that simply has the job of calling your main application with enough authorization data to handle security in the same context as your regular app, but this middle layer would in itself not be authorized. You will then just have to make sure that this app is not accessible to users outside of the firewall.

Authentication in a SharePoint environment

We are developing a Intranet portal that uses integrated authentication, but a few sections of the site will be exposed to users who are not in the domain. For those users we plan to use anonymous access. However, our display logic for the entire application is based on the user logged into the portal, so we are not fully comfortable with this approach. The URL has to be same for both types of users and transitioning between both the environments has to be seamless.
We tried using user controls in pages to authenticate but things didnt pan out. When the page is reached the standard windows authentication grey box pops up.
Is there any way to intercept the request at the IIS level like an HTTP application?
If applicable we would disable anonymous access and for unauthenticated users we will impersonate with a least privileged domain account and redirect to the home page.
SharePoint isn't really designed for the scenario you describe of mixing types of authentication. It dedicates a web application to one type of authentication. You can then 'extend' that web application to use another type of authentication on another address. For example, your intranet portal would use Windows authentication. It could then be extended to use anonymous authentication on another port or domain name.
One option for what you describe is to configure two separate web applications. One is for users that need to authenticate. The other is for anonymous access. Configure the content in the appropriate locations and link between the two as necessary. Users within your domain should not receive a login prompt when connecting to the authenticated site if you use this approach. Users outside your domain will receive a login box and won't be able to access.
Consider using forms authentication for users outside your domain if they need to access your intranet. (Once again the 'forms authenticated' part of your site would be extended to a unique domain name or port.) This would mean they will be prompted to enter their credentials in a form on the page when first connecting.
Read more about authentication on the Authentication Resource Center.
A couple of final points... If you can use SharePoint's default authentication mechanisms rather than writing your own controls, use them as they are well tested and secure. Also, don't be tempted to change SharePoint's IIS settings unless you are certain there is no other way to do what you need. SharePoint regularly updates these itself and may overwrite your changes (or give you grief in other ways).

How to open a link from one web app to another already authenticated?

We have one web application (sharepoint) that collects information from disparate sources. We would like to be able to link users to the main websites of those various sources and have them pre-authenticated. I.E. they enter their credentials for the other sources (which are a number of different types LDAP, AD and home grown!) and we retrieve some information for them, and remember there details (Possibly Single Sign-on to keep em nice and safe). The user can then click a link that will open the full app in another window already authenticated.
Is this even likely to be possible?
Office Server has a Single-Sign-On api as a builtin feature. you may want to look into that. It enables you to register user credentials securely, and to access it at runtime.
You need to act as a web browser acts to different sites with storing credentials (usually in cookies) locally. Use therefore a a proper client library with cookie support. This could go probably for most of sites. There are sites using HTTP authentication, which are also easier to access from appropriate client libraries. The most demanding can be access to SSL websites, but again, most client HTTP libraries cover that nowadays as well.
All you need now is just to prepare your web application to act as a proxy to all those separate web resources. How exactly this is done in Sharepoint, well, I hope others will answer that...
True Single Sign-on is a big task. Wikipedia describes common methods and links to a few SSO projects.
If you want something lighter, I've used this approach in the past:
Create a table to store temporary security tokens somewhere that all apps can access.
From the source app (Sharepoint in your case), on request of an external app, save a security token (maybe a guid, tight expiration, and userid) in the token table.
Redirect to a request broker page/handler in the destination app. Include the final page requested and the guid in the request.
In the broker, look up the security token. If it exists and hasn't expired, authenticate, authorize, and redirect to the final page if everything is good. If not, send a permissions err.
Security-wise, a guid should be near impossible to guess. You can shrink risk by letting the tokens expire very quickly - it shouldn't take more than a few seconds to call the broker.
If the destination app uses Windows Auth and doesn't have role-based logic, you shouldn't have to do much. Just redirect and let your File/UrlAuthorization handle it. You can handle role-based permissions with the security token db if required.

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