title: AWS Cognito user authentication Missing required parameter SRP_A
body: <p>I am trying to use AWS Cognito services for user authentication through <em>ruby</em> SDK.</p>
  
  <p>I could able to sign_up, confirm sign_up process using the methods</p>
  
  <pre><code>  resp = client.sign_up({ client_id: "ClientIdType",
                            secret_hash: "SecretHashType",
                            username: "UsernameType",
                            password: "PasswordType",
                            user_attributes: [{ name:"AttributeNameType", 
                                      value: "AttributeValueType",
                                       }],
                            validation_data: [{
                            name: "AttributeNameType",
                            value: "AttributeValueType",
                                    }]
                            })
  </code></pre>
  
  <p>and confirm_sign_up using </p>
  
  <pre><code>  resp = client.confirm_sign_up({client_id: "ClientIdType",
                                   secret_hash: "SecretHashType",
                                   username: "UsernameType",
                                   confirmation_code: "ConfirmationCodeType"
                                  })
  </code></pre>
  
  <p>But while trying to sign in the user through initiate_auth I am getting an error <strong>Missing required parameter SRP_A</strong></p>
  
  <pre><code>cog_provider.initiate_auth({client_id: "xxxxxxxxx", auth_parameters: { username: "xxx", password: "xxx"}, auth_flow: "USER_SRP_AUTH"})
  </code></pre>
  
  <p>What does SRP_A indicate where to find it.</p>
  
  <p>I have searched for this problem and It is suggested to use the <code>admin_initiate_auth</code> method for signing in a user which I don't believe a best practice.</p>