ActiveDirectoryServicePrincipalAccessToken: password/token not propagated to driver

sqlcmd advertises ActiveDirectoryServicePrincipalAccessToken via --authentication-method (see the help string in cmd/sqlcmd/sqlcmd.go around line 454), but the method does not actually work end-to-end.

Root cause

The go-mssqldb azuread connector for this method expects the pre-obtained bearer token to arrive in the connection string as the password. sqlcmd's pkg/sqlcmd/connect.go only attaches url.UserPassword(UserName, Password) to the URL for a specific set of methods (SqlPassword, ActiveDirectoryPassword, ActiveDirectoryServicePrincipal, ActiveDirectoryApplication, ActiveDirectoryClientAssertion). ActiveDirectoryServicePrincipalAccessToken is not in that list, so the value of -P / SQLCMDPASSWORD is silently dropped and the driver receives no token.

Repro

SQLCMDPASSWORD=<a valid AAD access token> sqlcmd -S <server> --authentication-method ActiveDirectoryServicePrincipalAccessToken -U <ignored>

Driver fails because no token was passed.

Suggested fix

Add ActiveDirectoryServicePrincipalAccessToken (and audit other azuread methods for the same gap) to the password-propagation branch in pkg/sqlcmd/connect.go.

Context

Surfaced in #639 while updating README docs to enumerate the supported --authentication-method values.

Start in pkg/sqlcmd/connect.go at the password-propagation branch and compare its listed authentication methods with ActiveDirectoryServicePrincipalAccessToken. Reproduce with the SQLCMDPASSWORD command from the issue, then verify the token reaches the driver and audit the other azuread methods for the same gap.