Yes, it is possible to connect to an Access Web App. I assume that you know how to get the server, database, username and password information from Access, but if not here is how.
Enable Connections for your Access Web App
- Open the Access Web App in the Access client
- Click the File tab > Info > click Manage within the Connections group
- If your Access App is on SharePoint Online, select From Any Location or From My Location to allow connections. Note: If you are on an IPv6 network, you will only have the option to connect From Any Location. In an on-premise installation, these options are not available.
- Select either Enable Read-Only Connection or Enable Read-Write Connection
- Depending on the previous selection, select either View Read-Only Connection Information or View Read-Write Connection Information
- Copy and paste the Server, Database, UserName and Password values into Notepad or Word, or leave the Connection Information window open so you can copy and paste the information from it later.
Then in PowerApps the source type to use is SQL Azure, and you will be asked for a connection string. Use the following
Server=tcp:MYSERVER.database.windows....,1433;Database=MYDATABASE;User ID=MYUSER;Password=MYPASSWORD;Encrypt=True;TrustServerCertificate=False;Connection Timeout=30;
This worked very well for me. Please let me know if anything is not clear.