Unable to validate credentials error
When you install or update Azure AD Connect, the following error appears:
Unable to validate credentials. An unexpected error has occurred. The underlying connection was closed: could not establish trust relationship for the SSL/TLS secure channel
Identity and solve the problem
To fully understand the underlying issue, I recommend you to read this.
The sources of this problem may be (non-exhaustive list):
- TLS version used
On my side, the problem was a proxy issue on https://login.windows.net:
After the proxy was reconfigured, the connection from Azure AD Connect to Azure AD is OK.