Fix a couple of instances where we are using LIST verb (#6026)

* Fix a couple of instances where we are using LIST verb

We specify it for the wrapping lookup function but for broader
compatibility with proxies and such we want to filter it to a GET. In a
couple of places we weren't doing that, so this updates those locations.

api/sys_plugins.go

@@ -42,6 +42,12 @@ func (c *Sys) ListPlugins(i *ListPluginsInput) (*ListPluginsResponse, error) {
 	}
 
 	req := c.c.NewRequest(method, path)
+	if method == "LIST" {
+		// Set this for broader compatibility, but we use LIST above to be able
+		// to handle the wrapping lookup function
+		req.Method = "GET"
+		req.Params.Set("list", "true")
+	}
 
 	ctx, cancelFunc := context.WithCancel(context.Background())
 	defer cancelFunc()
@@ -55,9 +61,10 @@ func (c *Sys) ListPlugins(i *ListPluginsInput) (*ListPluginsResponse, error) {
 	defer resp.Body.Close()
 
 	// We received an Unsupported Operation response from Vault, indicating
-	// Vault of an older version that doesn't support the READ method yet.
-	if resp.StatusCode == 405 && req.Method == "GET" {
-		req.Method = "LIST"
+	// Vault of an older version that doesn't support the GET method yet;
+	// switch it to a LIST.
+	if resp.StatusCode == 405 {
+		req.Params.Set("list", "true")
 		resp, err := c.c.RawRequestWithContext(ctx, req)
 		if err != nil {
 			return nil, err

api/sys_policy.go

@@ -10,6 +10,10 @@ import (
 
 func (c *Sys) ListPolicies() ([]string, error) {
 	r := c.c.NewRequest("LIST", "/v1/sys/policies/acl")
+	// Set this for broader compatibility, but we use LIST above to be able to
+	// handle the wrapping lookup function
+	r.Method = "GET"
+	r.Params.Set("list", "true")
 
 	ctx, cancelFunc := context.WithCancel(context.Background())
 	defer cancelFunc()