3. In C:\Solr\solr-8.4.0\server\etc add the following Powershell script and save it as solrssl.ps1:

param(
	[string]$KeystoreFile = 'solr-ssl.keystore.jks',
	[string]$KeystorePassword = 'secret',
	[string]$SolrDomain = 'localhost',
	[switch]$Clobber
)

$ErrorActionPreference = 'Stop'

### PARAM VALIDATION
if($KeystorePassword -ne 'secret') {
	Write-Error 'The keystore password must be "secret", because Solr apparently ignores the parameter'
}

if((Test-Path $KeystoreFile)) {
	if($Clobber) {
		Write-Host "Removing $KeystoreFile..."
		Remove-Item $KeystoreFile
	} else {
		$KeystorePath = Resolve-Path $KeystoreFile
		Write-Error "Keystore file $KeystorePath already existed. To regenerate it, pass -Clobber."
	}
}

$P12Path = [IO.Path]::ChangeExtension($KeystoreFile, 'p12')
if((Test-Path $P12Path)) {
	if($Clobber) {
		Write-Host "Removing $P12Path..."
		Remove-Item $P12Path
	} else {
		$P12Path = Resolve-Path $P12Path
		Write-Error "Keystore file $P12Path already existed. To regenerate it, pass -Clobber."
	}
}

try {
	$keytool = (Get-Command 'C:\Program Files\Java\jdk1.8.0_261\bin\keytool.exe').Source
} catch {
	$keytool = Read-Host "keytool.exe not on path. Enter path to keytool (found in JRE bin folder)"

	if([string]::IsNullOrEmpty($keytool) -or -not (Test-Path $keytool)) {
		Write-Error "Keytool path was invalid."
	}
}

### DOING STUFF

Write-Host ''
Write-Host 'Generating JKS keystore...'
& $keytool -genkeypair -alias solr-ssl -keyalg RSA -keysize 2048 -keypass $KeystorePassword -storepass $KeystorePassword -validity 9999 -keystore $KeystoreFile -ext SAN=DNS:$SolrDomain,IP:127.0.0.1 -dname "CN=$SolrDomain, OU=Enginnering, O=Verndale, L=Quito, ST=Pichincha, C=EC"

Write-Host ''
Write-Host 'Generating .p12 to import to Windows...'
& $keytool -importkeystore -srckeystore $KeystoreFile -destkeystore $P12Path -srcstoretype jks -deststoretype pkcs12 -srcstorepass $KeystorePassword -deststorepass $KeystorePassword

Write-Host ''
Write-Host 'Trusting generated SSL certificate...'
$secureStringKeystorePassword = ConvertTo-SecureString -String $KeystorePassword -Force -AsPlainText
$root = Import-PfxCertificate -FilePath $P12Path -Password $secureStringKeystorePassword -CertStoreLocation Cert:\LocalMachine\Root
Write-Host 'SSL certificate is now locally trusted. (added as root CA)'

Write-Host ''
Write-Host '########## NEXT STEPS ##########' -ForegroundColor Green
Write-Host ''
Write-Host '1. Copy your keystore to $SOLR_HOME\server\etc (MUST be here)' -ForegroundColor Green

if(-not $KeystoreFile.EndsWith('solr-ssl.keystore.jks')) {
	Write-Warning 'Your keystore file is not named "solr-ssl.keystore.jks"'
	Write-Warning 'Solr requires this exact name, so make sure to rename it before use.'
}

$KeystorePath = Resolve-Path $KeystoreFile
Write-Host ''
Write-Host '2. Add the following lines to your solr.in.cmd:' -ForegroundColor Green
Write-Host ''
Write-Host "set SOLR_SSL_KEY_STORE=etc/solr-ssl.keystore.jks" -ForegroundColor Yellow
Write-Host "set SOLR_SSL_KEY_STORE_PASSWORD=$KeystorePassword" -ForegroundColor Yellow
Write-Host "set SOLR_SSL_TRUST_STORE=etc/solr-ssl.keystore.jks" -ForegroundColor Yellow
Write-Host "set SOLR_SSL_TRUST_STORE_PASSWORD=$KeystorePassword" -ForegroundColor Yellow
Write-Host ''
Write-Host 'Done!'

You need to replace C:\Program Files\Java\jdk1.8.0_261\bin\keytool.exe path that match your installed Java JDK.

4. Then you need to run the following powershell script that is located at C:\Solr\solr-8.4.0\server\etc

.\solrssl.ps1

5. When execution is done, you will see solr-ssl.keystore.jks and solr-ssl.keystore.p12 files generated.

6. Edit C:\Solr\solr-8.4.0\bin\solr.in.cmd file and uncomment the following lines:

set SOLR_SSL_KEY_STORE=etc/solr-ssl.keystore.jks
set SOLR_SSL_KEY_STORE_PASSWORD=secret
set SOLR_SSL_TRUST_STORE=etc/solr-ssl.keystore.jks
set SOLR_SSL_TRUST_STORE_PASSWORD=secret
set SOLR_SSL_KEY_STORE_TYPE=JKS
set SOLR_SSL_TRUST_STORE_TYPE=JKS

7. Extract NSSM zip file into C:\nssm-2.24

9. Finally, run the following command

nssm install