Inject @CanonicalWebUrl instead of reading from config

Change-Id: I2d68a7672079c53eac8070145523fe91e028d358

src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java b/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java
index a58ef8a..837b4cc 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java
@@ -14,10 +14,14 @@
 
 package com.googlesource.gerrit.plugins.saml;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+
 import com.google.common.base.Strings;
 import com.google.common.collect.Iterators;
 import com.google.common.collect.Sets;
+import com.google.gerrit.common.Nullable;
 import com.google.gerrit.extensions.restapi.Url;
+import com.google.gerrit.server.config.CanonicalWebUrl;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.inject.Inject;
@@ -78,6 +82,7 @@
   @Inject
   SamlWebFilter(
       @GerritServerConfig Config gerritConfig,
+      @CanonicalWebUrl @Nullable String canonicalUrl,
       SitePaths sitePaths,
       SamlConfig samlConfig,
       SamlMembership samlMembership)
@@ -108,7 +113,6 @@
     samlClientConfig.setMaximumAuthenticationLifetime(samlConfig.getMaxAuthLifetimeAttr());
 
     saml2Client = new SAML2Client(samlClientConfig);
-    String callbackUrl = gerritConfig.getString("gerrit", null, "canonicalWebUrl") + SAML_CALLBACK;
     httpUserNameHeader = getHeaderFromConfig(gerritConfig, "httpHeader");
     httpDisplaynameHeader = getHeaderFromConfig(gerritConfig, "httpDisplaynameHeader");
     httpEmailHeader = getHeaderFromConfig(gerritConfig, "httpEmailHeader");
@@ -126,8 +130,8 @@
               + "are required.");
     }
     userNameToLowerCase = gerritConfig.getBoolean("auth", "userNameToLowerCase", false);
-
-    saml2Client.setCallbackUrl(callbackUrl);
+    checkNotNull(canonicalUrl, "gerrit.canonicalWebUrl must be set in gerrit.config");
+    saml2Client.setCallbackUrl(canonicalUrl + SAML_CALLBACK);
   }
 
   @Override