SSRS Legacy Report Running with no Data Source?

I've taken over the SSRS reports in our organisation and have the responsibility of developing new reports. I can do this (although not as well as the previous incumbent coming as I do from more of an SQL background).
Anyway, I'm having a problem with login credentials for some reports I've developed; we have a bespoke solution provided by our application vendor which passes credentials through to the reporting server. For some legacy reports this works fine and the reports open. However, the new reports I have created prompt for an SSRS login, UNLESS I have already opened one of the reports that does work. It seems that running a report that does work stores the credentials meaning that subsequent report requests do not require SSRS login.
So, what I would like to do is figure out why a working report does not require login credentials and see if I can replicate the setup in my new reports. Looking at one of the reports in BIDS, I can see that there is no data source shown, either embedded or shared. Obviously the report will not run in BIDS. However, the same report runs perfectly happily in Report Builder 3.0. I can't see any connection strings hidden anywhere, no parameters or variables appear to be set up, so I'm just wondering how it is possible for that report to work with no data source?

For information, here is a screenshot of the report in Report Builder:

Report Builder Design
And the Report results:

Report Results
Karl_markAsked:
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lcohanDatabase AnalystCommented:
"Data source credentials that you enter in the Data Source Properties Dialog Box, Credentials (Report Builder) page for an embedded data source.
These credentials are used by the report server to make a data connection to the external data source. For some types of data sources, credentials can be stored securely on the report server. These credentials enable other users to run the report without providing credentials for the underlying data connection."

https://msdn.microsoft.com/en-CA/library/ms160330(v=sql.105).aspx

For the SSRS reports that don't require to login most likely the credentials are stored within the report under security option when they were created/compiled/deployed in BIDS.

https://msdn.microsoft.com/en-CA/library/ms160330(v=sql.105).aspx
Karl_markAuthor Commented:
Thanks Icohan. The setup is as follows:

1. User credentials are passed from third-party app to SSRS allowing access to server.
2. Data source for reports is then connected via a SQL user account.

The reports that I have developed use a shared datasource held on the reporting server and log in using the SQL user account. I'm not sure where the other reports are connecting to SQL; I don't have access to the reporting server itself other than the logfiles (which don't reveal much when the user is prompted for a password) so I'll have to go through the DBA to find out if there are credentials held on the server. The problem is that the dba has also changed since the reports were initially set up (of course! Nothing is ever easy!).

Interestingly, I downloaded the Data Set from Reporting Services and when I opened it in Report Builder I was prompted for credentials. That gives me something to chew on!

Thanks for getting me thinking Icohan; I'll report back on what I find.
lcohanDatabase AnalystCommented:
I recommend to have a look at "Report Server Diagnostic Reports" and download/install a copy as it is extremely useful, safe and easy to use - I'm using it on production servers since SQL/SSRS 2005.
you can find it here and I know it may require to subscribe/login in order to get it but the site is safe and useful plus you can unsubscribe to not receive any of their mails at later time.
http://www.sqlservercentral.com/articles/Reporting+Services+(SSRS)/69257/
All you will have to do is to download then copy and unzip "SSRS Diagnostics Report Pack.zip" (bottom of the page just under Resources) to the SSRS server, create a shared data source DS_REPORTSERVER then import the RDL’s.

As far as existing older reports you can't do much really without having acces to the report RDL's or folder/solution if they were built in BIDS and you should also be able to find the way the new reports authenticate VS old reports authentication. I'm thinking old ones impersonate the NT login of the users running the "...bespoke solution provided by our application vendor which passes credentials through to the reporting server" therefor no login prompt required as they are set already in SSRS security.

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Karl_markAuthor Commented:
Thanks Icohan. I'll take a look at that Diagnostics Tool; it looks extremely useful in the screenshots!
I haven't found the solution to my problem but am going down the route of having the third-party app developer look at the authentication and doing some tweaks.
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