Download plugin from here : saml_authentication.zip
Step 1. Go to /var/www/html/concrete/packages folder and extract the zip file
Step 2. /var/www/html/concrete/packages/saml_authentication should look like :
Step 3. Go to Admin > Extend concrete5 > Click INSTALL SAML Authentication Plugin
Step 4. Go to Admin > System & Settings > Authentication Types
Step 5. Edit saml settings and click on enable button
Step 6. Go to Admin > System & Settings > Authentication Types and drag SAML authentication to the top.
Step 7. Go to your concrete login page and you should see SSO login button there.