Standardize environment variable names

... that are more like typical environment variables. Reasonably unique and upper case.

Deprecate other methods. The point of a connector method is to make sure all clients of the same library uses the same environments, thereby eliminating the pain of setting credentials per app.

Allowing the app to specify the environment variable names defeat this purpose.

src/main/java/org/kohsuke/github/GitHubBuilder.java

@@ -9,9 +9,13 @@ import java.io.IOException;
 import java.net.HttpURLConnection;
 import java.net.Proxy;
 import java.net.URL;
+import java.util.Locale;
+import java.util.Map.Entry;
 import java.util.Properties;
 
 /**
+ *
+ *
  * @since 1.59
  */
 public class GitHubBuilder {
@@ -60,6 +64,11 @@ public class GitHubBuilder {
             throw (IOException)new IOException("Failed to resolve credentials from ~/.github or the environment.").initCause(cause);
     }
 
+    /**
+     * @deprecated
+     *      Use {@link #fromEnvironment()} to pick up standard set of environment variables, so that
+     *      different clients of this library will all recognize one consistent set of coordinates.
+     */
     public static GitHubBuilder fromEnvironment(String loginVariableName, String passwordVariableName, String oauthVariableName) throws IOException {
         return fromEnvironment(loginVariableName, passwordVariableName, oauthVariableName, "");
     }
@@ -70,6 +79,11 @@ public class GitHubBuilder {
        		p.put(propName, v);
     }
 
+    /**
+     * @deprecated
+     *      Use {@link #fromEnvironment()} to pick up standard set of environment variables, so that
+     *      different clients of this library will all recognize one consistent set of coordinates.
+     */
     public static GitHubBuilder fromEnvironment(String loginVariableName, String passwordVariableName, String oauthVariableName, String endpointVariableName) throws IOException {
     	Properties env = new Properties();
     	loadIfSet(loginVariableName,env,"login");
@@ -78,10 +92,34 @@ public class GitHubBuilder {
         loadIfSet(endpointVariableName,env,"endpoint");
     	return fromProperties(env);
     }
-    
+
+    /**
+     * Creates {@link GitHubBuilder} by picking up coordinates from environment variables.
+     *
+     * <p>
+     * The following environment variables are recognized:
+     *
+     * <ul>
+     *     <li>GITHUB_LOGIN: username like 'kohsuke'
+     *     <li>GITHUB_PASSWORD: raw password
+     *     <li>GITHUB_OAUTH: OAuth token to login
+     *     <li>GITHUB_ENDPOINT: URL of the API endpoint
+     * </ul>
+     *
+     * <p>
+     * See class javadoc for the relationship between these coordinates.
+     *
+     * <p>
+     * For backward compatibility, the following environment variables are recognized but discouraged:
+     * login, password, oauth
+     */
     public static GitHubBuilder fromEnvironment() throws IOException {
     	Properties props = new Properties();
-    	props.putAll(System.getenv());
+        for (Entry<String, String> e : System.getenv().entrySet()) {
+            String name = e.getKey().toLowerCase(Locale.ENGLISH);
+            if (name.startsWith("github_")) name=name.substring(7);
+            props.put(name,e.getValue());
+        }
         return fromProperties(props);
     }