consistent auth token for validator apis (#13747)

* wip

* fixing tests

* adding more tests especially to handle legacy

* fixing linting

* fixing deepsource issues and flags

* fixing some deepsource issues,pathing issues, and logs

* some review items

* adding additional review feedback

* updating to follow updates from https://github.com/ethereum/keymanager-APIs/pull/74

* adjusting functions to match changes in keymanagers PR

* Update validator/rpc/auth_token.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/rpc/auth_token.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/rpc/auth_token.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* review feedback

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

api/BUILD.bazel

@@ -1,11 +1,24 @@
-load("@prysm//tools/go:def.bzl", "go_library")
+load("@prysm//tools/go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "go_default_library",
     srcs = [
         "constants.go",
         "headers.go",
+        "jwt.go",
     ],
     importpath = "github.com/prysmaticlabs/prysm/v5/api",
     visibility = ["//visibility:public"],
+    deps = [
+        "//crypto/rand:go_default_library",
+        "@com_github_ethereum_go_ethereum//common/hexutil:go_default_library",
+        "@com_github_pkg_errors//:go_default_library",
+    ],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = ["jwt_test.go"],
+    embed = [":go_default_library"],
+    deps = ["//testing/require:go_default_library"],
 )