One of the more powerful features in the new Power BI preview is the ability to connect your Power BI dashboard to an on-premises instance of SQL Server Analysis Services. This is done by installing a connector on-premises that connects to bot the SSAS server(s) and to the Power BI service. Installation is straightforward, but quite often the first attempt to connect to the data results in the “oh-so-helpful” error message, “something went wrong”.
The message isn’t very helpful, unless you’re speaking with a support representative.
I have found that the problem in most cases is that the user connecting to the data does not have sufficient rights on the SSAS server, or the server does not understand who the user is. This may very well be the same user that was used to connect from the SSAS Connector back into the service, but that doesn’t matter. The problem is that SSAS does not know about that identity.
To explain, first, we need to consider how the connector is registered.
When the connector is registered, two sets of credentials are provided. One credential is used to connect the connector to the SSAS server. This is an Windows credential (typically in the form of DOMAIN\username, and it must be an Administrator on the SSAS server. The reason for this requirement is that it will be used to funnel all Connector queries to the SSAS server, and it uses the EFFECTIVEUSERNAME feature in SSAS. EFFECTIVEUSERNAME requires admin level access.
The second credential is used to connect the connector to the Power BI service. This one is used to register the connector with the service so that it can be used by dashboard authors, and isn’t extensively used afterward. This credential will be an Organizational Account (i.e. an Office 365 identity/Azure Active Directory) and needs to have enough rights to register a data source with Power BI.
Once registered, it works as follows.
When a dashboard user interacts with the dashboard, or accesses the data source, a request is sent to the connector with the credentials of the user making the request. The connector then establishes a connection with the SSAS server, using the admin credentials registered with the connector, and issues the query using the EFFECTIVEUSERNAME parameter, which basically means “run this query using the provided user’s credentials”. The user provided is the one making the request. This allows for per-user level security for Power BI, but unfortunately, it is what typically causes the error above.
The issue is that SSAS only understands Windows (NTLM and Kerberos) credentials. Without doing anything else, it has no idea what an Organizational ID is. So how can it work at all? There are two ways.
The first, is that your domain can be federated with Azure Active directory, specifically with the Azure Active directory that your Power BI (Office 365) tenant is using. Once federation is complete, your AD domain (domainxxx.com) will be registered and trusted with your internal NTLM/Kerberos domain and your users will be mapped to their Azure ID identities. SSAS will then understand who they are, and if granted permission, they will be able to access SSAS data via the Power BI dashboard. This is the only supported method, and is what should be used in a production environment. There is however another way.
If AD federation is not an option in the short term, or you simply need to get a development or demonstration environment spun up, it is possible to “hack” your active directory to allow SSAS to understand the organizational IDs. First, the AD domain is registered directly with Active directory, then the Active Directory users can be set to use that directory. The key part is that the user name in the internal AD (ie DOMAIN\xxx) must match the user portion of the Azure AD account (ie firstname.lastname@example.org). The entire procedure is outline very well by Greg Galloway in this article, and I won’t repeat it here.
Going back to the original error, it would be nice if it could be a little more descriptive. I’d be happy with “Access Denied”. These are early days, and the product is still in preview – I expect this will change. Security also may not be the only cause of this error, but it’s the only one that I’ve seen thus far.