This merges the `SENT_LOGIN7_WITH_STANDARD_LOGIN`,
`SENT_LOGIN7_WITH_NTLM` and `SENT_NTLM_RESPONSE` states into a single
`SENT_LOGIN7` state.

Both domain and workstation are optional according to the MS-NLMP
specification, so we should not require a domain to be given.

This should improve/ease the use of NTLM auth with Azure SQL Server.

SSPI is the interface name / API that's used for all authentication
providers.. "native" is a more fitting name because it depends on the
operating system's native APIs to provide security support.

Each auth provider can have different configuration options, and by
keeping them specific to each provider, we can make sure the list of
options that can be passed to the tedious constructor does not grow any
larger than it already is.

Also remove the native auth provider specific `securityPackage` option.

This logic is already covered by the NTLM auth provider tests.

This buffer is used for all SSPI authentication types, not just for
NTLM.

We only perform handshaking after receiving a message, and no further TDS messages should be received during the handshake, so there is no need to do an explicit check in the auth provider.

This fixes a potentially security relevant issue where `tedious` would
send username and password in plaintext via the LOGIN7 token, even if
the `domain` option was specified and the credentials were sent as
hashes via NTLM as well.

…se'd.

When no username and password are specified, and the native auth
provider is supported, `tedious` will now use it automatically.

This reverts commit 9f8e637.

…ggable-auth-providers

…ggable-auth-providers

…ggable-auth-providers