Add support for loading token by filepath or environment var

README.md

@@ -135,8 +135,16 @@ Conjur conjur = new Conjur(credentials);
 
 #### Authorization Token
 ```java
-String authTokenString = new String(Files.readAllBytes(Paths.get('path/to/conjur/authentication/token.json')));
-Token token = Token.fromJson(authTokenString);
+Token token = Token.fromFile(Paths.get('path/to/conjur/authentication/token.json'));
+Conjur conjur = new Conjur(token);
+```
+
+Alternatively, to use the `CONJUR_AUTHN_TOKEN_FILE` environment variable:
+```bash
+export CONJUR_AUTHN_TOKEN_FILE="path/to/conjur/authentication/token.json"
+```
+```java
+Token token = Token.fromEnv();
 Conjur conjur = new Conjur(token);
 ```
 

src/main/java/net/conjur/api/Token.java

@@ -17,6 +17,7 @@ public class Token {
     private static final DateTimeFormatter DATE_TIME_FORMATTER =
             // tokens use dates like 2013-10-01 18:48:32 UTC
             DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss ZZZ");
+    private static final String TOKEN_FILE_ENV_VARIABLE = "CONJUR_AUTHN_TOKEN_FILE";
 
     // Hold our fields in here to facilitate json serialization/deserialization
     private static class Fields {
@@ -123,6 +124,16 @@ public static Token fromJson(String json){
         return new Token(json);
     }
 
+    public static Token fromFile(Path filepath) {
+        String json = File.readAllBytes(filepath);
+        return fromJson(json);
+    }
+
+    public static Token fromEnv() {
+        String tokenFilePath = System.getenv(TOKEN_FILE_ENV_VARIABLE);
+        return fromFile(Paths.get(tokenFilePath));
+    }
+
     private String fromBase64(String base64){
         return new String(Base64.decodeBase64(base64), StandardCharsets.UTF_8);
     }