Connect to a DB by directly supplying access token

[RudraNirvan]

Refer to the example file (examples/azuread-service-principal-authtoken/service_principal_authtoken.go) to understand how it will work.

EOL CRLF difference is causing all the lines to be shown as changed, not sure if GitHub offers an option to ignore this while reviewing, suggestions are welcome.

Fixes #24.

[ghost]

All CLA requirements met.

[shueybubbles]

I think this scenario was supposed to be covered by the non-AAD-aware token provider interface here:

go-mssqldb/fedauth.go

Line 44 in f21bac1

func NewSecurityTokenConnector(config msdsn.Config, tokenProvider func(ctx context.Context) (string, error)) (*Connector, error) {

No need to bring in any azuread dependencies, just provide a function that provides the token

[RudraNirvan]

@shueybubbles yes, but how will a client of this library use it? This PR allows one to easily supply the token as a part of the connection string when connecting to the DB. Internally, you will notice that I am using the same NewSecurityTokenConnector.

Refer to the connection string in the example file: "server=%s;password=%s;port=%d;database=%s;fedauth=ActiveDirectoryServicePrincipalAccessToken;"

That's it, one will now only need to supply the access token as the password.

[RudraNirvan]

@shueybubbles For the access token to work, it needs to pass through the fedauth login workflow. Refer:

go-mssqldb/tds.go

Line 998 in f21bac1

case fe.FedAuthLibrary == FedAuthLibrarySecurityToken:

[codecov-commenter]

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