Allow usage of base64url encoding / Issue #34

docs/index.asciidoc

@@ -41,6 +41,7 @@ This plugin supports the following configuration options plus the <<plugins-{typ
 |=======================================================================
 |Setting |Input type|Required
 | <<plugins-{type}s-{plugin}-base64encode>> |<<boolean,boolean>>|No
+| <<plugins-{type}s-{plugin}-base64url>> |<<boolean,boolean>>|No
 | <<plugins-{type}s-{plugin}-concatenate_sources>> |<<boolean,boolean>>|No
 | <<plugins-{type}s-{plugin}-concatenate_all_fields>> |<<boolean,boolean>>|No
 | <<plugins-{type}s-{plugin}-key>> |<<string,string>>|No
@@ -63,6 +64,15 @@ filter plugins.
 When set to `true`, the `SHA1`, `SHA256`, `SHA384`, `SHA512` and `MD5` fingerprint methods will produce
 base64 encoded rather than hex encoded strings.
 
+[id="plugins-{type}s-{plugin}-base64url"]
+===== `base64url` 
+
+  * Value type is <<boolean,boolean>>
+  * Default value is `false`
+
+Requires `base64encode` to be set to `true`.
+When set to `true`, the base64url variant will be used, as described in [RFC4648 section 5](https://tools.ietf.org/html/rfc4648#section-5).
+
 [id="plugins-{type}s-{plugin}-concatenate_sources"]
 ===== `concatenate_sources` 
 

lib/logstash/filters/fingerprint.rb

@@ -41,6 +41,10 @@ class LogStash::Filters::Fingerprint < LogStash::Filters::Base
   # base64 encoded rather than hex encoded strings.
   config :base64encode, :validate => :boolean, :default => false
 
+  # When set to `true`, the base64url encoder https://tools.ietf.org/html/rfc4648 is used.
+  # Requires `base64encode` to be enabled.
+  config :base64url, :validate => :boolean, :default => false
+
   # The fingerprint method to use.
   #
   # If set to `SHA1`, `SHA256`, `SHA384`, `SHA512`, or `MD5` and a key is set,
@@ -156,14 +160,23 @@ def fingerprint_openssl(data)
     # in JRuby 1.7.11 outputs as ASCII-8BIT
     if @key.nil?
       if @base64encode
-        @digest.base64digest(data.to_s).force_encoding(Encoding::UTF_8)
+        if @base64url
+          # Borrowed by Base64 implementation
+          @digest.base64digest(data.to_s).tr("+/", "-_").force_encoding(Encoding::UTF_8)
+        else
+          @digest.base64digest(data.to_s).force_encoding(Encoding::UTF_8)
+        end
       else
         @digest.hexdigest(data.to_s).force_encoding(Encoding::UTF_8)
       end
     else
       if @base64encode
         hash = OpenSSL::HMAC.digest(@digest, @key, data.to_s)
-        Base64.strict_encode64(hash).force_encoding(Encoding::UTF_8)
+        if @base64url
+          Base64.urlsafe_encode64(hash).force_encoding(Encoding::UTF_8)
+        else 
+          Base64.strict_encode64(hash).force_encoding(Encoding::UTF_8)
+        end
       else
         OpenSSL::HMAC.hexdigest(@digest, @key, data.to_s).force_encoding(Encoding::UTF_8)
       end

spec/filters/fingerprint_spec.rb

@@ -99,6 +99,23 @@
     end
   end
 
+  describe "fingerprint string with SHA1 algorithm and base64url encoding" do
+    config <<-CONFIG
+      filter {
+        fingerprint {
+          source => ["clientip"]
+          method => 'SHA256'
+          base64encode => true
+          base64url => true
+        }
+      }
+    CONFIG
+
+    sample("clientip" => "123.123.123.123") do
+      insist { subject.get("fingerprint") } == "TavKshB2bjXwPncSDmmG1ubUdSsqn_IpgLklPQJggNg="
+    end
+  end
+
   describe "fingerprint string with SHA1 HMAC algorithm and base64 encoding" do
     config <<-CONFIG
       filter {
@@ -116,6 +133,24 @@
     end
   end
 
+  describe "fingerprint string with SHA1 HMAC algorithm and base64url encoding" do
+    config <<-CONFIG
+      filter {
+        fingerprint {
+          source => ["clientip"]
+          key => "longencryptionkey"
+          method => 'SHA1'
+          base64encode => true
+          base64url => true
+        }
+      }
+    CONFIG
+
+    sample("clientip" => "123.123.123.123") do
+      insist { subject.get("fingerprint") } == "_cYKzEdz3FrFaf-3j8uTyWMHl_Q="
+    end
+  end
+
   describe "fingerprint string with SHA256 algorithm" do
     config <<-CONFIG
       filter {