Use Omniauthable user model with admin role

Gemfile.lock

@@ -85,11 +85,14 @@ GEM
     docile (1.3.1)
     erubi (1.8.0)
     execjs (2.7.0)
+    faraday (0.15.4)
+      multipart-post (>= 1.2, < 3)
     ffi (1.9.25)
     ffi (1.9.25-x64-mingw32)
     ffi (1.9.25-x86-mingw32)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
+    hashie (3.6.0)
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
     jbuilder (2.8.0)
@@ -100,6 +103,7 @@ GEM
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
     json (1.8.6)
+    jwt (2.1.0)
     loofah (2.2.3)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
@@ -116,6 +120,8 @@ GEM
     msgpack (1.2.6-x64-mingw32)
     msgpack (1.2.6-x86-mingw32)
     multi_json (1.13.1)
+    multi_xml (0.6.0)
+    multipart-post (2.0.0)
     mysql2 (0.5.2)
     mysql2 (0.5.2-x64-mingw32)
     mysql2 (0.5.2-x86-mingw32)
@@ -126,6 +132,21 @@ GEM
       mini_portile2 (~> 2.4.0)
     nokogiri (1.10.1-x86-mingw32)
       mini_portile2 (~> 2.4.0)
+    oauth2 (1.4.1)
+      faraday (>= 0.8, < 0.16.0)
+      jwt (>= 1.0, < 3.0)
+      multi_json (~> 1.3)
+      multi_xml (~> 0.5)
+      rack (>= 1.2, < 3)
+    omniauth (1.9.0)
+      hashie (>= 3.4.6, < 3.7.0)
+      rack (>= 1.6.2, < 3)
+    omniauth-github (1.3.0)
+      omniauth (~> 1.5)
+      omniauth-oauth2 (>= 1.4.0, < 2.0)
+    omniauth-oauth2 (1.6.0)
+      oauth2 (~> 1.1)
+      omniauth (~> 1.9)
     orm_adapter (0.5.0)
     rack (2.0.6)
     rack-test (1.1.0)
@@ -240,6 +261,8 @@ DEPENDENCIES
   jbuilder (~> 2.8.0)
   jquery-rails (~> 4.3.3)
   mysql2 (~> 0.5.2)
+  omniauth
+  omniauth-github
   rails (= 5.2.2)
   rails-controller-testing
   rails-i18n (~> 5.1.3)