Implemented TOTP Secret Backend (#2492)

* Initialized basic outline of TOTP backend using Postgresql backend as template

* Updated TOTP backend.go's structure and help string

* Updated TOTP path_roles.go's structure and help strings

* Updated TOTP path_role_create.go's structure and help strings

* Fixed typo in path_roles.go

* Fixed errors in path_role_create.go and path_roles.go

* Added TOTP secret backend information to cli commands

* Fixed build errors in path_roles.go and path_role_create.go

* Changed field values of period and digits from uint to int, added uint conversion of period when generating passwords

* Initialized TOTP test file based on structure of postgresql test file

* Added enforcement of input values

* Added otp library to vendor folder

* Added test steps and cleaned up errors

* Modified read credential test step, not working yet

* Use of vendored package not allowed - Test error

* Removed vendor files for TOTP library

* Revert "Removed vendor files for TOTP library"

This reverts commit fcd0309.

* Hopefully fixed vendor folder issue with TOTP Library

* Added additional tests for TOTP backend

* Cleaned up comments in TOTP backend_test.go

* Added default values of period, algorithm and digits to field schema

* Changed account_name and issuer fields to optional

* Removed MD5 as a hash algorithm option

* Implemented requested pull request changes

* Added ability to validate TOTP codes

* Added ability to have a key generated

* Added skew, qr size and key size parameters

* Reset vendor.json prior to merge

* Readded otp and barcode libraries to vendor.json

* Modified help strings for path_role_create.go

* Fixed test issue in testAccStepReadRole

* Cleaned up error formatting, variable names and path names. Also added some additional documentation

* Moveed barcode and url output to key creation function and did some additional cleanup based on requested changes

* Added ability to pass in TOTP urls

* Added additional tests for TOTP server functions

* Removed unused QRSize, URL and Generate members of keyEntry struct

* Removed unnecessary urlstring variable from pathKeyCreate

* Added website documentation for TOTP secret backend

* Added errors if generate is true and url or key is passed, removed logger from backend, and revised parameter documentation.

* Updated website documentation and added QR example

* Added exported variable and ability to disable QR generation, cleaned up error reporting, changed default skew value, updated documentation and added additional tests

* Updated API documentation to inlude to exported variable and qr size option

* Cleaned up return statements in path_code, added error handling while validating codes and clarified documentation for generate parameters in path_keys

builtin/logical/totp/backend.go

@@ -0,0 +1,37 @@
+package totp
+
+import (
+	"strings"
+
+	"github.com/hashicorp/vault/logical"
+	"github.com/hashicorp/vault/logical/framework"
+)
+
+func Factory(conf *logical.BackendConfig) (logical.Backend, error) {
+	return Backend(conf).Setup(conf)
+}
+
+func Backend(conf *logical.BackendConfig) *backend {
+	var b backend
+	b.Backend = &framework.Backend{
+		Help: strings.TrimSpace(backendHelp),
+
+		Paths: []*framework.Path{
+			pathListKeys(&b),
+			pathKeys(&b),
+			pathCode(&b),
+		},
+
+		Secrets: []*framework.Secret{},
+	}
+
+	return &b
+}
+
+type backend struct {
+	*framework.Backend
+}
+
+const backendHelp = `
+The TOTP backend dynamically generates time-based one-time use passwords.
+`