diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index 156069f..aee764c 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -1,14 +1,48 @@
 class SessionsController < ApplicationController
-  def new
-    redirect_uri = url_for(action: :create, only_path: false)
+  def hca_new
+    redirect_uri = url_for(action: :hca_create, only_path: false)
+
+    redirect_to User.hca_authorize_url(redirect_uri),
+      host: "https://auth.hackclub.com",
+      allow_other_host: "https://auth.hackclub.com"
+  end
+
+  def hca_create
+    if params[:error].present?
+      Rails.logger.error "Slack OAuth error: #{params[:error]}"
+      Sentry.capture_message("Slack OAuth error: #{params[:error]}")
+      redirect_to root_path, alert: "Failed to authenticate with Slack. Error ID: #{Sentry.last_event_id}"
+      return
+    end
+
+    redirect_uri = url_for(action: :hca_create, only_path: false)
+
+    @user = User.from_hca_token(params[:code], redirect_uri)
+
+    # if @user&.persisted?
+    if @user&.persisted?
+      session[:user_id] = @user.id
+
+      if @user.data_migration_jobs.empty?
+        MigrateUserFromHackatimeJob.perform_later(@user.id)
+      end
+
+      redirect_to root_path, notice: "Successfully signed in with Slack! Welcome!"
+    else
+      redirect_to root_path, alert: "Failed to authenticate with Hack Club Auth!"
+    end
+  end
+
+  def slack_new
+    redirect_uri = url_for(action: :slack_create, only_path: false)
     Rails.logger.info "Starting Slack OAuth flow with redirect URI: #{redirect_uri}"
-    redirect_to User.authorize_url(redirect_uri, close_window: params[:close_window].present?, continue_param: params[:continue]),
+    redirect_to User.slack_authorize_url(redirect_uri, close_window: params[:close_window].present?, continue_param: params[:continue]),
                 host: "https://slack.com",
                 allow_other_host: "https://slack.com"
   end
 
-  def create
-    redirect_uri = url_for(action: :create, only_path: false)
+  def slack_create
+    redirect_uri = url_for(action: :slack_create, only_path: false)
 
     if params[:error].present?
       Rails.logger.error "Slack OAuth error: #{params[:error]}"
diff --git a/app/models/user.rb b/app/models/user.rb
index e80e533..a531766 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -8,7 +8,7 @@ class User < ApplicationRecord
 
   after_create :create_signup_activity
   before_validation :normalize_username
-  encrypts :slack_access_token, :github_access_token
+  encrypts :slack_access_token, :github_access_token, :hca_access_token
 
   validates :slack_uid, uniqueness: true, allow_nil: true
   validates :github_uid, uniqueness: { conditions: -> { where.not(github_access_token: nil) } }, allow_nil: true
@@ -327,7 +327,18 @@ class User < ApplicationRecord
       })
   end
 
-  def self.authorize_url(redirect_uri, close_window: false, continue_param: nil)
+  def self.hca_authorize_url(redirect_uri)
+    params = {
+      redirect_uri:,
+      client_id: ENV["HCA_CLIENT_ID"],
+      response_type: "code",
+      scope: "email"
+    }
+
+    URI.parse("#{HCAService.host}/oauth/authorize?#{params.to_query}")
+  end
+
+  def self.slack_authorize_url(redirect_uri, close_window: false, continue_param: nil)
     state = {
       token: SecureRandom.hex(24),
       close_window: close_window,
@@ -355,6 +366,43 @@ class User < ApplicationRecord
     URI.parse("https://github.com/login/oauth/authorize?#{params.to_query}")
   end
 
+  def self.from_hca_token(code, redirect_uri)
+    # Exchange code for token
+    response = HTTP.post("#{HCAService.host}/oauth/token", form: {
+      client_id: ENV["HCA_CLIENT_ID"],
+      client_secret: ENV["HCA_CLIENT_SECRET"],
+      redirect_uri: redirect_uri,
+      code: code,
+      grant_type: "authorization_code"
+    })
+
+    data = JSON.parse(response.body.to_s)
+
+    access_token = data["access_token"]
+    return nil if access_token.nil?
+
+    # get user info
+    identity = ::HCAService.me(access_token)
+    # find by HCA ID
+    @user = User.find_by_hca_id(identity["id"]) unless identity["id"].blank?
+    # find by slack_id
+    @user ||= User.find_by_slack_uid(identity["slack_id"]) unless identity["slack_id"].blank?
+    # find by email
+    @user ||= begin
+                EmailAddress.find_by(email: identity["email"])&.user unless identity["email"].blank?
+              end
+
+    # update scopes if user exists
+    @user.update(hca_scopes: identity["scopes"], hca_id: identity["id"]) if @user
+
+    # if no user, create one
+    @user ||= begin
+                u = User.create!(hca_id: identity["id"], slack_uid: identity["slack_id"], hca_scopes: identity["scopes"])
+                EmailAddress.create!(email: identity["email"], user: u) unless identity["email"].blank?
+                u
+              end
+  end
+
   def self.from_slack_token(code, redirect_uri)
     # Exchange code for token
     response = HTTP.post("https://slack.com/api/oauth.v2.access", form: {
diff --git a/app/services/hca_service.rb b/app/services/hca_service.rb
new file mode 100644
index 0000000..fba4c8c
--- /dev/null
+++ b/app/services/hca_service.rb
@@ -0,0 +1,18 @@
+module HCAService
+  def host
+    if Rails.env.production?
+      "https://auth.hackclub.com"
+    else
+      "https://hca.dinosaurbbq.org"
+    end
+  end
+
+  def me(user_token)
+    raise ArgumentError, "user_token is required" unless user_token
+
+    response = HTTP.auth("Bearer " + user_token)
+                   .get(host + "/api/v1/me")
+    JSON.parse(response.body)
+  end
+  module_function :me, :host
+end
diff --git a/app/views/static_pages/index.html.erb b/app/views/static_pages/index.html.erb
index c004de5..03e50c4 100644
--- a/app/views/static_pages/index.html.erb
+++ b/app/views/static_pages/index.html.erb
@@ -24,9 +24,16 @@
   <% else %>
     <h1 class="font-bold mt-1 mb-1 text-5xl text-center">Track How Much You <span class="text-primary">Code</span></h1>
     <div class="flex flex-col w-full max-w-[50vw] mx-auto mb-22">
+      <% if params[:hca_auth].present? %>
+        <%= link_to hca_auth_path, class: "inline-flex items-center justify-center px-6 py-3 rounded text-white font-bold cursor-pointer border-none w-full my-2 bg-primary" do %>
+          <img src="/images/slack.png" class="h-8 w-8 mr-2 bg-white rounded-full p-1">
+          <span class="hidden md:flex">Sign in with Hack Club</span>
+        <% end %>
+      <% end %>
+
       <%= link_to slack_auth_path, class: "inline-flex items-center justify-center px-6 py-3 rounded text-white font-bold cursor-pointer border-none w-full my-2 bg-primary" do %>
         <img src="/images/slack.png" class="h-8 w-8 mr-2 bg-white rounded-full p-1">
-        <span class="hidden md:flex">Sign in with Hack Club Slack</span>
+        <span class="hidden md:flex">Sign in with Slack</span>
       <% end %>
 
       <div class="flex items-center my-4">
diff --git a/config/initializers/inflections.rb b/config/initializers/inflections.rb
index 3860f65..bbeb218 100644
--- a/config/initializers/inflections.rb
+++ b/config/initializers/inflections.rb
@@ -11,6 +11,6 @@
 # end
 
 # These inflection rules are supported but not enabled by default:
-# ActiveSupport::Inflector.inflections(:en) do |inflect|
-#   inflect.acronym "RESTful"
-# end
+ActiveSupport::Inflector.inflections(:en) do |inflect|
+  inflect.acronym "HCA"
+end
diff --git a/config/routes.rb b/config/routes.rb
index 65c8cd8..981a298 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -74,8 +74,10 @@ Rails.application.routes.draw do
   get "/what-is-hackatime", to: "static_pages#what_is_hackatime"
 
   # Auth routes
-  get "/auth/slack", to: "sessions#new", as: :slack_auth
-  get "/auth/slack/callback", to: "sessions#create"
+  get "/auth/hca", to: "sessions#hca_new", as: :hca_auth
+  get "/auth/hca/callback", to: "sessions#hca_create"
+  get "/auth/slack", to: "sessions#slack_new", as: :slack_auth
+  get "/auth/slack/callback", to: "sessions#slack_create"
   get "/auth/github", to: "sessions#github_new", as: :github_auth
   get "/auth/github/callback", to: "sessions#github_create"
   delete "/auth/github/unlink", to: "sessions#github_unlink", as: :github_unlink
diff --git a/db/migrate/20251202221230_add_hca_fields_to_users.rb b/db/migrate/20251202221230_add_hca_fields_to_users.rb
new file mode 100644
index 0000000..c940fb9
--- /dev/null
+++ b/db/migrate/20251202221230_add_hca_fields_to_users.rb
@@ -0,0 +1,7 @@
+class AddHCAFieldsToUsers < ActiveRecord::Migration[8.1]
+  def change
+    add_column :users, :hca_id, :string
+    add_column :users, :hca_scopes, :string, array: true, default: []
+    add_column :users, :hca_access_token, :string
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 3f47171..07c08a0 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2025_12_01_161700) do
+ActiveRecord::Schema[8.1].define(version: 2025_12_02_221230) do
   create_schema "pganalyze"
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
@@ -550,6 +550,9 @@ ActiveRecord::Schema[8.1].define(version: 2025_12_01_161700) do
     t.string "github_uid"
     t.string "github_username"
     t.integer "hackatime_extension_text_type", default: 0, null: false
+    t.string "hca_access_token"
+    t.string "hca_id"
+    t.string "hca_scopes", default: [], array: true
     t.string "mailing_address_otc"
     t.text "slack_access_token"
     t.string "slack_avatar_url"