Error unprotecting the session cookie in an ASP.NET Core MVC application.

The new ASP.NET Core MVC framework automatically displays a message for the user to accept the application’s privacy policy. The default message is “Use this space to summarize your privacy and cookie use policy.” No cookies are saved in the user’s browser until they click the Accept button.

Even after accepting the terms, if the browser contains old, stale cookies the application may not be able to save cookies. The log contains

warn: Microsoft.AspNetCore.Session.SessionMiddleware[7]
Error unprotecting the session cookie.
System.Security.Cryptography.CryptographicException: The key … was not found in the key ring.

If the web application works in a new incognito window, clear the old cookies in your browser.

In Google Chrome

  1. In the Chrome menu select Clear Browsing Data
  2. On the Clear browsing data page select All time, and Cookies and other site data

 

 

Set the environment for an ASP.NET Core MVC web application

When the ASP.NET Core MVC web application starts, reads the name of the environment for an environment variable of the host computer. The compiled application contains the configuration for all supported environments, making possible to build and deploy the same artifact in every environment.

If the ASPNETCORE_ENVIRONMENT environment variable is not defined, the Production environment settings are loaded.

In Visual Studio the web application project sets the value on the Debug tab.

To set the environment on the server

Windows

To set the value globally that is preserved after restart

Command prompt

  1. Open the command prompt window and execute
    setx ASPNETCORE_ENVIRONMENT Development /M

PowerShell

  1. Open a PowerShell window and execute
    [Environment]::SetEnvironmentVariable("ASPNETCORE_ENVIRONMENT", "Development", "Machine")

macOS

  1. Add to the .bashrc or .bash_profile file
    export ASPNETCORE_ENVIRONMENT=Development

 

Configure the ASP.NET Core MVC web application

Create the environment-specific appsettings.json files

  1. In the web application project click the arrow next to the appsettings.json file to reveal the Development configuration file
  2. Right-click the appsettings.Development.json file and select Copy

  3. Right click the web application project and select Paste

  4. Rename the appsettings – Copy.Development.json file to appsettings.Production.json

  5. The file will automatically move under the appsettings.json file

Edit the configuration files

  1. Open the appsettings.Production.json file and add the connection string
    {
        "ConnectionStrings": {
            "DefaultConnection": "Server=MY_DATABASE_URL;Database=MY_DATABASE_NAME;Username=MY_USERNAME;Password=MY_PASSWORD"
        }
    }
    
    

 

Enable .NET Core Entity Framework Linq query execution

When we create a new .NET Core class it only contains the using System; reference.

To enable Linq database queries in a .NET Core project, add using System.Linq;

using System;
using System.Linq;

To enable the usage of .Include() in the Linq queries, add

using Microsoft.EntityFrameworkCore;

 

Return values to the controller in the model from the ASP.NET MVC view

When we create an ASP.NET MVC web application, the model (an object) is the easiest way to return values from the view to the controller.

For the view to be able to return the values in the model, make sure the model contains properties, not fields, for every value with { get; set; }

public class MyViewModel
{
    public string ID { get; set; }
}

Add the model to the view at the top of the .cshtml file

IMPORTANT!!! To return values for properties that do not have controls on the page, like IDs that are not displayed, add a hidden field to the view.

@model MyViewModel
<form  asp-action="Index" asp-controller="My">
    <input asp-for=@Model.ID type="hidden" >
</form>

Send the data in the model to the view from the get method in the controller

public class MyController : Controller
{
    public IActionResult Index()
    {
         MyViewModel model = new MyViewModel();
         model.ID = "MY_ID";
         return View(model);
    }
}

Read the value from the model in the post method of the controller and send the model back

public class MyController : Controller
{
    [HttpPost, ValidateAntiForgeryToken]
    public IActionResult Index(MyViewModel model)
    {
        string ID = model.ID;
...
        return View(model);
    }
}

 

Error loading table definition of a PostgreSQL table

When a PostgreSQL table name contains uppercase letters there is no known way to get the table definition SQL script.

When we right-click a table name in SQLPro for Postgres the has an uppercase letter and select Script as, CREATE to, New query window

we get the error message

/*
* Error loading table definition.
* ERROR: relation “public.users” does not exist
*/

As the error message tells us, PostgreSQL is looking for the table name with all lowercase letters.


The pg_dump utility acts the same way.

pg_dump -s -h MY_SERVER_ADDRESS -U M_USERNAME -t Users MY_DATABASE

The error message is

pg_dump: no matching tables were found


The same process works if the table name only contains lowercase letters.

Convert an existing PostgreSQL database to all lowercase table and column names

To avoid similar errors caused by upper case letters in table and column names, convert the existing database definition to all lowercase

    1. Backup your database from the command prompt
      PGPASSWORD=MY_PASSWORD pg_dump -h MY_DATABASE_ADDRESS -U MY_DATABSE_USER -f MY_BACKUP_FILENAME.bak MY_DATABASE_NAME
    2. Open the backup file in a text editor
    3. Add underscores to the table and column names to match the .NET entity framework user identity processes.
      1. The PostgreSQL driver converts the first letter of all lowercase table and column names to upper-case and the letter that follows an underscore. For example, asp_net_users will be converted to AspNetUsers.
        1. Replace the table names with TableName -> table_name ( leave __EFMigrationsHistory as is)
        2. Replace the column names with “ColumnName” -> “column_name”
        3. Replace the primary key names with PK_ -> pk_
        4. Replace the index names with IX_ -> ix_
        5. Replace the foreign key names with FK_ -> fk_
    4. Drop the database. In SQL Pro for Postgres
      1. Right-click the database and select Drop database
    5. Re-create the database. In SQL Pro for Postgres
      1. Rith-click the server name and select Create database
    6. Import the modified backup file from the command prompt
      PGPASSWORD=MY_PASSWORD psql -h MY_DATABASE_ADDRESS -U MY_DATABSE_USER -d MY_DATABASE_NAME -f MY_BACKUP_FILENAME.bak
    7. Reverse engineer the database back to the .NET data layer project
      1. Delete the class files that correspond to the database tables
      2. Delete the MY_DATABSEContext.cs file
      3. Import execute the command in the data layer project directory
        dotnet ef dbcontext scaffold --force "Host=MY_DATABASE_ADDRESS;Database=MY_DATABASE_NAME;Username=MY_DATABSE_USER;Password=MY_PASSWORD" Npgsql.EntityFrameworkCore.PostgreSQL

Reverse engineer a database with AspNetCore in Visual Studio

For some reason the .NETCore designers did not think, that developers want to follow best practices by separating the data layer from the presentation layer.

The Entity framework out of the box only works if the database is accessed from the main application project.

When we try to reverse engineer a PostgreSQL database from a class library with the command:

cd MY_CLASS_LIBRARY_DIRECTORY
dotnet ef dbcontext scaffold "Host=localhost;Database=MY_DATABASE_NAME;Username=MY_USERNAME;Password=MY_PASSWORD" Npgsql.EntityFrameworkCore.PostgreSQL

we get the error message:

The specified framework version ‘2.1’ could not be parsed
The specified framework ‘Microsoft.NETCore.App’, version ‘2.1’ was not found.
– Check application dependencies and target a framework version installed at:
/usr/local/share/dotnet/
– Installing .NET Core prerequisites might help resolve this problem:
http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
– The .NET Core framework and SDK can be installed from:
https://aka.ms/dotnet-download
– The following versions are installed:
2.0.0 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
2.1.2 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
2.1.3 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

The problem is, that the …runtimeconfig.json files are only automatically generated in the bin/netcoreapp2.1 directory of the main application project, those are missing from all class libraries.

To enable the automatic generation of the …runtimeconfig.json files, add a line to the <PropertyGroup> section of the data layer class library project (.csproj) file.

<PropertyGroup>
...
<GenerateRuntimeConfigurationFiles>True</GenerateRuntimeConfigurationFiles>
...
</PropertyGroup>

 

Use two GitHub accounts on the same computer

Many developers have multiple GitHub accounts. One for personal projects, and another one for their work or business. There is a way to access multiple accounts simultaneously from the same computer. Only one account at a time can be configured using the HTTP connection, but we can configure the rest of the accounts using SSH.

There are many great articles on this topic, but most of them only provide partial instructions on how to set up multiple GitHub accounts on the same computer. In this post, I will document all the necessary steps to set up two accounts.

Usually, you don’t have much control over what GitHub connectivity is used for the company account, it can be dictated by the customer or your workplace, but you can always control what to use for your personal account. With SSH you can specify all aspects of your personal account, so you can leave the default SSH or HTTP connection for the business or company account.

In this post, we will set up two accounts with SSH connection. Even if the business account currently uses HTTP, it makes sense to set up SSH for that account too, in case they will switch to SSH at a later time.

Create two keys

    1. Open a terminal window and start the authentication agent to avoid the “Could not open a connection to your authentication agent” error later
       eval `ssh-agent -s`
    2. Create the personal SSH key
      ssh-keygen -t rsa -C "MY_PERSONAL_EMAIL@ADDRESS"

      when asked for the file name by the “Enter file in which to save the key“prompt, save the key as id_rsa_pers

    3. Add the personal key to the authentication agent
      ssh-add id_rsa_pers
    4. Create the business SSH key
      ssh-keygen -t rsa -C "MY_COMPANY_EMAIL@ADDRESS"

      when asked for the file name by the “Enter file in which to save the key“prompt, save the key as id_rsa_COMPANY_NAME

    5. Add the business key to the authentication agent
      ssh-add id_rsa_COMPANY_NAME

If you want to use existing keys from another location

If you already have the keys at another location or at another user account, copy the ~/.ssh directory to the new home directory. Do the same if you want to use the same keys in sudo mode. In that case switch to sudo mode with

sudo -i

Copy the .ssh directory

cd ~
cp -r /home/OTHER_USER/.ssh .

Set the file permissions

If you have copied the keys from another location, the file permissions may not set correctly. If the key permissions are too open, Linux displays the message:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: UNPROTECTED PRIVATE KEY FILE! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Permissions 0755 for ‘/home/MY_USER_NAME/.ssh/id_rsa_pers’ are too open.
It is required that your private key files are NOT accessible by others.
This private key will be ignored.
Load key “/home/MY_USER_NAME/.ssh/id_rsa_pers”: bad permissions
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Set the file permissions. Execute the following statements in a terminal window

  1. Navigate to the .ssh directory
    cd ~/.ssh
  2. Set the key file permissions
    sudo chmod 600 ~/.ssh/id_rsa
    sudo chmod 600 ~/.ssh/id_rsa.pub
    sudo chmod 600 ~/.ssh/id_rsa_pers
    sudo chmod 600 ~/.ssh/id_rsa_pers.pub
    sudo chmod 600 ~/.ssh/id_rsa_COMPANY_NAME
    sudo chmod 600 ~/.ssh/id_rsa_COMPANY_NAME.pub
    
  3. Set the nown_host file permission
    sudo chmod 644 ~/.ssh/known_hosts
  4. Set the directory permission
    sudo chmod 755 ~/.ssh
  5. Start the authentication agent to avoid the “Could not open a connection to your authentication agent” error later
     eval `ssh-agent -s`
  6. Register the keys
    ssh-add id_rsa
    ssh-add id_rsa_pers
    ssh-add id_rsa_COMPANY_NAME

Configure SSH to use the two new keys

  1. Create the SSH config file
    touch ~/.ssh/config
  2. Open the ~/.ssh/config file with a text editor
  3. Add the following lines
    #Personal GitHub
    Host github-pers
      HostName github.com
      User MY_PERSONAL_GITHUB_USERNAME
      IdentityFile ~/.ssh/id_rsa_pers
    
    #Company GitHub
    Host github.com
      HostName github.com
      User MY_COMPANY_GITHUB_USERNAME
      IdentityFile ~/.ssh/id_rsa_COMPANY_NAME
    

Upload the keys to your GitHub accounts

  1. Log into the GitHub website with your personal credentials
  2. In the upper right corner click the down arrow next to your icon, and select Settings
  3. On the left side select SSH and GPG keys
  4. Click the New SSH key button
  5. Type a name for the key,  paste the contents of the ~/.ssh/id_rsa_pers.pub public key file into the text area, and click the Add SSH key button
  6. Log into Github with your company credentials
  7. Upload the id_rsa_COMPANY_NAME.pub public key file as explained above.

Create a personal repository

  1. Create a new folder, personal-test, and add a file to it on your computer
  2. Initialize the Git repository in the folder
    git init
    git add .
    git commit -m "Initial commit"
  3. Log into your personal GitHub account
  4. Create a new repository, and name it personal-test
  5. On the confirmation page click the SSH button
  6. Copy the …or push an existing… code to a text editor
  7. Edit the origin address to match the “Host” of the personal section in the ~/.ssh/config file, and execute the commands
    git remote add origin git@github-pers:MY_PERSONAL_GITHUB_USERNAME/personal-test.git
    git push -u origin master

Company repositories

For your company account use the default HTTP or SSH GitHub repository address without any modifications.

Change the AWS account to launch instances with Chef Test Kitchen

The Chef SDK contains Test Kitchen, that can launch server instances to test your Chef cookbooks. Test Kitchen uses the “chef_zero” provisioner to use your workstation as the virtual Chef server.

To switch Test Kitchen to launch instances in another AWS account

  1. In the .kitchen.yml file update the
    1. availability_zone
    2. subnet_id
    3. aws_ssh_key_id
    4. security_group_ids. Make sure the management ports are open:
      1. for Linux: port 22 for SSH, or
      2. for Windows: port 5985 – 5986 for WinRM and port 3389 for Remote Desktop
    5. ssh_key
  2. In the default.rb attribute file update the
    1. …[‘aws_profile’]
  3. In the ~/.aws/credentials file update the
    1. [default] section

Copy files between Linux machines

The rsync command allows you to copy files using SSH connection, between your workstation and another Linux machine. You have to be logged into one of the machines, this command cannot copy files between two remote machines.

To copy a file from a remote server to your local workstation, execute

rsync -avz -e "ssh -i SSH_KEY_NAME" USER_NAME@SOURCE_IP:/SOURCE_DIRECTORY/SOURCE_FILE_NAME TARGET_DIRECTORY

To copy a file to a remote server, swap the source and target definitions after the SSH_KEY_NAME option.

Using tmux terminal multiplexer

The tmux terminal multiplexer allows us to open multiple terminal windows in the same SSH session and continue the command execution even when we log out of the SSH session. This way we can execute long-running copy commands overnight without keeping the SSH session open.

Install tmux

On CentOS family Linux

yum install tmux

To start tmux and attach to the last session

tmux a

To keep the current session active

To continue the session execution even when you log out of the server, detach from the session before closing the connection. See the commands below.

Commands

To switch to binding mode

ctrl-b

Commands in binding mode

d detach
% vertical split
horizontal split
arrows move between panes
c new window
p previous window
n next window
l last used pane
q display pane numbers
[ enable scroll with arrow keys or pgup, pgdown
q quit scroll mode
x close the pane (will ask you to press “y” to confirm)

Zooming

cmd-shift + zoom in
cmd-shift – zoom out
cmd-shift 0 (zero) 100% zoom