Make http client and its filter non-blocking

src/main/java/micronaut/http/AuthClient.java

@@ -5,6 +5,7 @@
 import io.micronaut.http.annotation.QueryValue;
 import io.micronaut.http.client.annotation.Client;
 import io.reactivex.Flowable;
+import io.reactivex.Single;
 
 @Client("${auth.url}")
 public interface AuthClient {
@@ -16,5 +17,5 @@ Flowable<ValidateTokenResponse> validateToken(
     );
 
     @Post(value = "/issue/token", consumes = "application/json")
-    Token retrieveToken(@Body AuthRequest issueTokenRequest);
+    Single<Token> retrieveToken(@Body AuthRequest issueTokenRequest);
 }

src/main/java/micronaut/http/AuthenticateFilter.java

@@ -21,6 +21,8 @@ public AuthenticateFilter(TokenIssuer tokenIssuer) {
 
     @Override
     public Publisher<? extends HttpResponse<?>> doFilter(MutableHttpRequest<?> request, ClientFilterChain chain) {
-        return chain.proceed(request.bearerAuth(tokenIssuer.retrieveToken().getAccessToken()));
+        return tokenIssuer.retrieveToken()
+            .map(token -> request.bearerAuth(token.getAccessToken()))
+            .flatMapPublisher(chain::proceed);
     }
 }

src/main/java/micronaut/http/TokenIssuer.java

@@ -1,6 +1,7 @@
 package micronaut.http;
 
 import io.micronaut.context.annotation.Property;
+import io.reactivex.Single;
 
 import javax.inject.Singleton;
 
@@ -18,7 +19,7 @@ public TokenIssuer(
         this.clientId = clientId;
     }
 
-    public Token retrieveToken() {
+    public Single<Token> retrieveToken() {
         return authClient.retrieveToken(new AuthRequest(clientId));
     }
 }