add EnvironmentVariableCredentialsProvider

Author: huiguangjun

src/AlibabaCloud.OSS.V2/Credentials/EnvironmentVariableCredentialsProvider.cs

@@ -0,0 +1,31 @@
+using System;
+
+namespace AlibabaCloud.OSS.V2.Credentials {
+    /// <summary>
+    /// Obtaining credentials from environment variables.
+    /// OSS_ACCESS_KEY_ID
+    /// OSS_ACCESS_KEY_SECRET
+    /// OSS_SESSION_TOKEN(Optional)
+    /// </summary>
+    public class EnvironmentVariableCredentialsProvider : ICredentialsProvider {
+        private readonly Credentials _credentials;
+        /// <summary>
+        /// Creates an instance of <see cref="EnvironmentVariableCredentialsProvider"/>
+        /// </summary>
+        public EnvironmentVariableCredentialsProvider() {
+            var ak = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
+            var sk = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
+            if (string.IsNullOrEmpty(ak) || string.IsNullOrEmpty(sk)) {
+                throw new ArgumentException("Credentials is null or empty");
+            }
+            var token = Environment.GetEnvironmentVariable("OSS_SESSION_TOKEN");
+
+            _credentials = new Credentials(ak, sk, token ?? "");
+        }
+
+        /// <inheritdoc/>
+        public Credentials GetCredentials() {
+            return _credentials;
+        }
+    }
+}