title: Postgres will not allow alter role superuser and my default user isn't superuser
body: <p>I cannot connect to Postgres using Elixir:</p>
  <pre><code>** (Mix) The database for PhoenixChat.Repo couldn't be created: FATAL 28P01 (invalid_password): password authentication failed for user &quot;postgres&quot;
  
  00:08:59.053 [error] GenServer #PID&lt;0.3214.0&gt; terminating
  ** (Postgrex.Error) FATAL 28P01 (invalid_password): password authentication failed for user &quot;postgres&quot;
      (db_connection) lib/db_connection/connection.ex:148: DBConnection.Connection.connect/2
      (connection) lib/connection.ex:622: Connection.enter_connect/5
      (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
  Last message: nil
  State: Postgrex.Protocol
  </code></pre>
  <p>I cannot understand how a database could allow users to be made without one being a superuser. From my usual user, it does not allow giving superuser role:</p>
  <pre><code>$ psql -U thisone --password
  Password for user thisone: 
  psql: FATAL:  Peer authentication failed for user &quot;thisone&quot;
  
  $ psql -U fakeuser
  psql: FATAL:  Peer authentication failed for user &quot;fakeuser&quot;
  
  cchilders=&gt; alter user postgres superuser;
  ERROR:  must be superuser to alter superusers
  cchilders=&gt; select rolname from pg_roles;
    rolname  
  -----------
   postgres
   cchilders
   fakeuser
   thisone
  (4 rows)
  
  $ psql -U postgres --password
  Password for user postgres: 
  psql: FATAL:  Peer authentication failed for user &quot;postgres&quot;
  </code></pre>
  <p>How can I give a user superuser in Postgres if there is no superuser?</p>