hotspot2: expose string constants for cert type and auth methods

So that we can use these constants in WifiService and the apps
as well in the future.

While there, remove auth method "CHAP" from the supported list,
since it is currenlty not supported by WifiService.

Bug: 34206769
Test: make -j32
Change-Id: Icadc3b13f2b135d51445d336116fbba86e96b70f
diff --git a/wifi/java/android/net/wifi/hotspot2/pps/Credential.java b/wifi/java/android/net/wifi/hotspot2/pps/Credential.java
index 620759d..2388841 100644
--- a/wifi/java/android/net/wifi/hotspot2/pps/Credential.java
+++ b/wifi/java/android/net/wifi/hotspot2/pps/Credential.java
@@ -122,12 +122,22 @@
         private static final int MAX_PASSWORD_BYTES = 255;
 
         /**
+         * Supported authentication methods.
+         * @hide
+         */
+        public static final String AUTH_METHOD_PAP = "PAP";
+        /** @hide */
+        public static final String AUTH_METHOD_MSCHAP = "MS-CHAP";
+        /** @hide */
+        public static final String AUTH_METHOD_MSCHAPV2 = "MS-CHAP-V2";
+
+        /**
          * Supported Non-EAP inner methods.  Refer to
          * Credential/UsernamePassword/EAPMethod/InnerEAPType in Hotspot 2.0 Release 2 Technical
          * Specification Section 9.1 for more info.
          */
-        private static final Set<String> SUPPORTED_AUTH =
-                new HashSet<String>(Arrays.asList("PAP", "CHAP", "MS-CHAP", "MS-CHAP-V2"));
+        private static final Set<String> SUPPORTED_AUTH = new HashSet<String>(
+                Arrays.asList(AUTH_METHOD_PAP, AUTH_METHOD_MSCHAP, AUTH_METHOD_MSCHAPV2));
 
         /**
          * Username of the credential.
@@ -348,8 +358,9 @@
     public static final class CertificateCredential implements Parcelable {
         /**
          * Supported certificate types.
+         * @hide
          */
-        private static final String CERT_TYPE_X509V3 = "x509v3";
+        public static final String CERT_TYPE_X509V3 = "x509v3";
 
         /**
          * Certificate SHA-256 fingerprint length.