auth: have cgit calculate login address

This way we're sure to use virtual root, or any other strangeness
encountered.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
diff --git a/cgit.c b/cgit.c
index be1265d..994957f 100644
--- a/cgit.c
+++ b/cgit.c
@@ -611,7 +611,8 @@
 		ctx->env.https ? ctx->env.https : "",
 		ctx->qry.repo ? ctx->qry.repo : "",
 		ctx->qry.page ? ctx->qry.page : "",
-		ctx->qry.url ? ctx->qry.url : "");
+		ctx->qry.url ? ctx->qry.url : "",
+		cgit_loginurl());
 }
 
 /* We intentionally keep this rather small, instead of looping and