Add ListUsers API to list all configured users in IAM (#6619)

pkg/madmin/API.md

@@ -40,7 +40,7 @@ func main() {
 |:----------------------------|:----------------------------|:--------------------------------------|:--------------------------|:------------------------------------|:------------------------------------|
 | [`ServiceStatus`](#ServiceStatus) | [`ServerInfo`](#ServerInfo) | [`Heal`](#Heal) | [`GetConfig`](#GetConfig) | [`AddUser()`](#AddUser) | [`SetAdminCredentials`](#SetAdminCredentials) |
 | [`ServiceSendAction`](#ServiceSendAction) | | | [`SetConfig`](#SetConfig) | [`AddUserPolicy`](#AddUserPolicy) | [`StartProfiling`](#StartProfiling) |
-| | |            | [`GetConfigKeys`](#GetConfigKeys) | [`DownloadProfilingData`](#DownloadProfilingData) |
+| | |            | [`GetConfigKeys`](#GetConfigKeys) | [`ListUsers`](#ListUsers) | [`DownloadProfilingData`](#DownloadProfilingData) |
 | | |            | [`SetConfigKeys`](#SetConfigKeys) |                                     |
 
 
@@ -375,6 +375,22 @@ __Example__
 	}
 ```
 
+<a name="ListUsers"></a>
+### ListUsers() (map[string]UserInfo, error)
+Lists all users on Minio server.
+
+__Example__
+
+``` go
+	users, err := madmClnt.ListUsers(); 
+    if err != nil {
+		log.Fatalln(err)
+	}
+    for k, v := range users {
+        fmt.Printf("User %s Status %s\n", k, v.Status)
+    }
+```
+
 ## 9. Misc operations
 
 <a name="SetAdminCredentials"></a>

pkg/madmin/user-commands.go

@@ -34,7 +34,7 @@ const (
 
 // UserInfo carries information about long term users.
 type UserInfo struct {
-	SecretKey string        `json:"secretKey"`
+	SecretKey string        `json:"secretKey,omitempty"`
 	Status    AccountStatus `json:"status"`
 }
 
@@ -63,6 +63,37 @@ func (adm *AdminClient) RemoveUser(accessKey string) error {
 	return nil
 }
 
+// ListUsers - list all users.
+func (adm *AdminClient) ListUsers() (map[string]UserInfo, error) {
+	reqData := requestData{
+		relPath: "/v1/list-users",
+	}
+
+	// Execute GET on /minio/admin/v1/list-users
+	resp, err := adm.executeMethod("GET", reqData)
+
+	defer closeResponse(resp)
+	if err != nil {
+		return nil, err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, httpRespToErrorResponse(resp)
+	}
+
+	data, err := DecryptData(adm.secretAccessKey, resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var users = make(map[string]UserInfo)
+	if err = json.Unmarshal(data, &users); err != nil {
+		return nil, err
+	}
+
+	return users, nil
+}
+
 // SetUser - sets a user info.
 func (adm *AdminClient) SetUser(accessKey, secretKey string, status AccountStatus) error {
 	data, err := json.Marshal(UserInfo{