Support trimming trailing slashes via a mount tuneable to support CMPv2 (#28752)

* Support trimming trailing slashes via a mount tuneable to support CMPv2

* changelog/

* Perform trimming in handleLoginRequest too

* Eagerly fetch the mount entry so we only test this once

* Add a mount match function that gets path and entry

* Update vault/request_handling.go

Co-authored-by: Steven Clark <steven.clark@hashicorp.com>

* more docs

* Some patches (from ENT) didnt apply

* patch fail

* Update vault/router.go

Co-authored-by: Steven Clark <steven.clark@hashicorp.com>

* PR feedback

* dupe

* another dupe

* Add support for enabling trim_request_trailing_slashes on mount creation

* Fix read mount api returning configuration for trim_request_trailing_slashes

* Fix test assertion

* Switch enable and tune arguments to BoolPtrVal to allow end-users to specify false flag

* Add trim-request-trailing-slashes to the auth enable API and CLI

---------

Co-authored-by: Steven Clark <steven.clark@hashicorp.com>

command/auth_tune.go

@@ -40,6 +40,7 @@ type AuthTuneCommand struct {
 	flagUserLockoutCounterResetDuration time.Duration
 	flagUserLockoutDisable              bool
 	flagIdentityTokenKey                string
+	flagTrimRequestTrailingSlashes      BoolPtr
 }
 
 func (c *AuthTuneCommand) Synopsis() string {
@@ -195,6 +196,11 @@ func (c *AuthTuneCommand) Flags() *FlagSets {
 		Usage: "Select the semantic version of the plugin to run. The new version must be registered in " +
 			"the plugin catalog, and will not start running until the plugin is reloaded.",
 	})
+	f.BoolPtrVar(&BoolPtrVar{
+		Name:   flagNameTrimRequestTrailingSlashes,
+		Target: &c.flagTrimRequestTrailingSlashes,
+		Usage:  "Whether to trim trailing slashes for incoming requests to this mount",
+	})
 
 	f.StringVar(&StringVar{
 		Name:    flagNameIdentityTokenKey,
@@ -306,6 +312,11 @@ func (c *AuthTuneCommand) Run(args []string) int {
 		if fl.Name == flagNameIdentityTokenKey {
 			mountConfigInput.IdentityTokenKey = c.flagIdentityTokenKey
 		}
+
+		if fl.Name == flagNameTrimRequestTrailingSlashes && c.flagTrimRequestTrailingSlashes.IsSet() {
+			val := c.flagTrimRequestTrailingSlashes.Get()
+			mountConfigInput.TrimRequestTrailingSlashes = &val
+		}
 	})
 
 	// Append /auth (since that's where auths live) and a trailing slash to