tpl/crypto: Add hmac

docs/content/en/functions/hmac.md

@@ -0,0 +1,34 @@
+---
+title: hmac
+linktitle: hmac
+description: Compute the cryptographic checksum of a message.
+godocref:
+date: 2020-05-29
+publishdate: 2020-05-29
+lastmod: 2020-05-29
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [hmac,checksum]
+signature: ["hmac HASH_TYPE KEY MESSAGE"]
+workson: []
+hugoversion:
+relatedfuncs: [hmac]
+deprecated: false
+aliases: [hmac]
+---
+
+`hmac` returns a cryptographic hash that uses a key to sign a message.
+
+```
+{{ hmac "sha256" "Secret key" "Hello world, gophers!"}},
+<!-- returns the string "b6d11b6c53830b9d87036272ca9fe9d19306b8f9d8aa07b15da27d89e6e34f40"
+```
+
+Supported hash functions:
+
+* md5
+* sha1
+* sha256
+* sha512