controller: support rate-limiting incoming requests

helps constraining resource usage and against flood attacks.

Signed-off-by: Ramkumar Chinchani <rchincha@cisco.com>

go.sum

@@ -708,6 +708,8 @@ github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f/go.mod h1:cu
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
 github.com/dgryski/trifles v0.0.0-20200323201526-dd97f9abfb48 h1:fRzb/w+pyskVMQ+UbP35JkH8yB7MYb4q/qhBarqZE6g=
 github.com/dgryski/trifles v0.0.0-20200323201526-dd97f9abfb48/go.mod h1:if7Fbed8SFyPtHLHbg49SI7NAdJiC5WIA09pe59rfAA=
+github.com/didip/tollbooth/v6 v6.1.1 h1:Nt7PvWLa9Y94OrykXsFNBinVRQIu8xdy4avpl99Dc1M=
+github.com/didip/tollbooth/v6 v6.1.1/go.mod h1:xjcse6CTHCLuOkzsWrEgdy9WPJFv+p/x6v+MyfP+O9s=
 github.com/dimchansky/utfbom v1.1.0/go.mod h1:rO41eb7gLfo8SF1jd9F8HplJm1Fewwi4mQvIirEdv+8=
 github.com/dimchansky/utfbom v1.1.1 h1:vV6w1AhK4VMnhBno/TPVCoK9U/LP0PkLCS9tbxHdi/U=
 github.com/dimchansky/utfbom v1.1.1/go.mod h1:SxdoEBH5qIqFocHMyGOXVAybYJdr71b1Q/j0mACtrfE=
@@ -1001,6 +1003,8 @@ github.com/go-openapi/validate v0.20.3 h1:GZPPhhKSZrE8HjB4eEkoYAZmoWA4+tCemSgINH
 github.com/go-openapi/validate v0.20.3/go.mod h1:goDdqVGiigM3jChcrYJxD2joalke3ZXeftD16byIjA4=
 github.com/go-piv/piv-go v1.9.0 h1:P6j2gjfP7zO7T3nCk/jwCgsvFRwB8shEqAJ4q85jgXc=
 github.com/go-piv/piv-go v1.9.0/go.mod h1:NZ2zmjVkfFaL/CF8cVQ/pXdXtuj110zEKGdJM6fJZZM=
+github.com/go-pkgz/expirable-cache v0.0.3 h1:rTh6qNPp78z0bQE6HDhXBHUwqnV9i09Vm6dksJLXQDc=
+github.com/go-pkgz/expirable-cache v0.0.3/go.mod h1:+IauqN00R2FqNRLCLA+X5YljQJrwB179PfiAoMPlTlQ=
 github.com/go-playground/assert/v2 v2.0.1/go.mod h1:VDjEfimB/XKnb+ZQfWdccd7VUvScMdVu0Titje2rxJ4=
 github.com/go-playground/locales v0.12.1/go.mod h1:IUMDtCfWo/w/mtMfIE/IG2K+Ey3ygWanZIBtBW0W2TM=
 github.com/go-playground/locales v0.13.0 h1:HyWk6mgj5qFqCT5fjGBuRArbVDfE4hi8+e8ceBS/t7Q=