Use pipe as extension URI separator (#2737)

It turns out period can be used in the URI, such as in
"urn:ietf:params:xml:ns:fee-0.12". I don't think pipe is used, at least
not according to EPP URI namespace naming convention.

Ideally we'd use serialization, but using the default serialization runs
the risk of it being platform/JDK dependent, so a new deployment might
not be able to deserialize existing cookies. A custom serializer that
guarantees stability would have been needed.

core/src/main/java/google/registry/flows/CookieSessionMetadata.java

@@ -103,7 +103,7 @@ public class CookieSessionMetadata extends SessionMetadata {
   @Override
   public Set<String> getServiceExtensionUris() {
     return Optional.ofNullable(data.getOrDefault(SERVICE_EXTENSIONS, null))
-        .map(s -> Splitter.on('.').splitToList(s))
+        .map(s -> Splitter.on(URI_SEPARATOR).splitToList(s))
         .map(ImmutableSet::copyOf)
         .orElse(ImmutableSet.of());
   }
@@ -125,7 +125,7 @@ public class CookieSessionMetadata extends SessionMetadata {
     if (serviceExtensionUris == null || serviceExtensionUris.isEmpty()) {
       data.remove(SERVICE_EXTENSIONS);
     } else {
-      data.put(SERVICE_EXTENSIONS, Joiner.on('.').join(serviceExtensionUris));
+      data.put(SERVICE_EXTENSIONS, Joiner.on(URI_SEPARATOR).join(serviceExtensionUris));
     }
   }
 

core/src/main/java/google/registry/flows/SessionMetadata.java

@@ -24,6 +24,8 @@ import java.util.Set;
 /** Object to allow setting and retrieving session information in flows. */
 public abstract class SessionMetadata {
 
+  protected static final char URI_SEPARATOR = '|';
+
   /**
    * Invalidates the session. A new instance must be created after this for future sessions.
    * Attempts to invoke methods of this class after this method has been called will throw {@code
@@ -50,7 +52,9 @@ public abstract class SessionMetadata {
     return toStringHelper(getClass())
         .add("clientId", getRegistrarId())
         .add("failedLoginAttempts", getFailedLoginAttempts())
-        .add("serviceExtensionUris", Joiner.on('.').join(nullToEmpty(getServiceExtensionUris())))
+        .add(
+            "serviceExtensionUris",
+            Joiner.on(URI_SEPARATOR).join(nullToEmpty(getServiceExtensionUris())))
         .toString();
   }