auth: use token.Type() instead of token.TokenType
auth: use token.Type() instead of token.TokenType

TokenType might be empty.

Change-Id: I8f57d208542c08b6d9c2d469b6ad2813953edefa
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2738513
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go