A connection was successfully established with the server, but then an error occurred during the login process.

[andrew-vdb]

Describe the bug

Unable to open trusted connection

A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.)'

To reproduce

await connection.OpenAsync();

Expected behavior

It should connect

Further technical details

Microsoft.Data.SqlClient version: 4.0
.NET target: .net 6
SQL Server version:

Operating system: Win 10

Workaround
Use System.Data.SqlClient, it works.... or use Microsoft.Data.SqlClient 3.0.1

[cheenamalhotra]

”Encrypt” is now true by default

[andrew-vdb]

Add
Encrypt=false
to connection string will work too

[RubberChickenParadise]

To anyone finding this, in my case it was due to the self signed server certificate. see #1210 (comment):

Systems using SQL Server's self-generated certificate will fail after this change and the user will have to buy a certificate or create a self-signed certificate, or change their connection string. If the change was made for scenarios where the user could not modify the connection string to enable encryption, then they are left having to get new certificates.

The fixes are:

1. disable encryption on the client connection string with Encrypt=false
2. blindly trust the server certificate with TrustServerCertificate=True
3. use an external certificate on the sql server that is signed by a certificate authority in the clients trusted certificate authorities.
   3b) if the sql server already has an externally signed certificate, trust the signing certificate authority on the client.