URLsigner

a PowerShell module to add digital signatures

to Google Static Maps and Static Street View URLs

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Installation

Copy the URLsigner folder containing the staticSigner.psm1 file to your PowerShell user module path

• On Windows systems, copy the URLsigner folder to $HOME\Documents\PowerShell\Modules
• On non-Windows systems, copy URLsigner to $HOME/.local/share/powershell/Modules

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Set default URL Signing Secret (optional)

To add a digital signature to a Google Static Maps or Static Street View URL, you need to use the URL Signing Secret from your Google API project.

The staticSigner.psm1 file has a dummy URL Signing Secret set as the default:
$script:secretKey = "aBcDeFgHiJkLmNoPqRsTuVwXyZ-="
This is the correct format for a Signing Secret and can be used to generate a sample signed URL, but the signed URL will not be valid.

You can specify a valid URL Signing Secret each time you import the module, or you can edit staticSigner.psm1 to include your URL Signing Secret as the default.

To set the default URL Signing Secret to the one from your Google Cloud project:

1. Go to the Maps APIs Credentials page of your API project.
2. Select the Maps Static API or Static Street View API from the list at the top marked "All Google Maps Platform APIs"
3. Copy the 28-character Current Secret (including the "=" sign at the end)
   
4. Open the URLsigner/URLsigner.psm1 file in a code editor
5. Find the line starting with
   $script:secretKey =
   and replace the dummy signing secret with the one from your project
6. Save the URLsigner.psm1 file

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Importing the module and preparing to sign URLs

After you've saved the URLsigner folder containing the URLsigner.psm1 file to your PowerShell profile path, you can import the module from a PowerShell command line:
PS> Import-Module URLsigner

Before signing a Static Maps or Static Street View URL, you need to run the Set-SecretKey command:
PS> Set-SecretKey "jdW0fdx88bGYVwTCxIjWSpBJMoo="

(this secret key has already been regenerated -- get your actual URL Signing Secret from the Maps-APIs Credentials page of your project)
If you've already edited URLsigner.psm1 to replace the dummy default key with your actual URL Signing Secret, you can use:
PS> Set-SecretKey
to use the default you've set.

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Signing a URL

After you've imported the module and run Set-SecretKey, you can use the signStaticUrl function to add a digital signature to a Static Maps or Static Street View URL:
PS> $url_1 = "https://maps.googleapis.com/maps/api/staticmap?center=Royal+Greenwich+Observatory,London,England&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U"

(note: this API key AIza...C1MMU has already been regenerated and is expired)

PS> signStaticUrl $url_1
https://maps.googleapis.com/maps/api/staticmap?center=Royal+Greenwich+Observatory,London,England&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U&signature=omVx1LZnFWT2kmnBXdwaUiDMNxE=

The URLsignermodule creates two aliases, Protect-StaticUrl and Protect-Url, for the signStaticUrl function:

PS> Protect-StaticUrl $url_1
https://maps.googleapis.com/maps/api/staticmap?center=Royal+Greenwich+Observatory,London,England&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U&signature=omVx1LZnFWT2kmnBXdwaUiDMNxE=

You can see that both signStaticUrl and Protect-StaticUrl generate the same signature omVx1LZnFWT2kmnBXdwaUiDMNxE= for $url_1

PS> $url_2 = "https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U"

PS> Protect-Url $url_2
https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U&signature=BhiRbuHKA-9TBW1kmeitFN1ObuA=

Re-signing a previously signed URL

If the URL was already signed using a different URL Signing Secret, the signStaticUrl function (and its aliases) will remove the old signature before creating a new signature and adding it to the URL:
PS> Set-SecretKey
$secretKey set to default value (edit URLsigner.psm1 to change default value)
PS> $signed_url = Protect-StaticUrl $url_2
PS> $signed_url
https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U&signature=JR7YxKgwk7gQjqhYWu3NFhydsW8=
PS> Set-SecretKey "jdW0fdx88bGYVwTCxIjWSpBJMoo="*
$secretKey has been set
PS> $signed_url = Protect-StaticUrl $signed_url
PS> $signed_url
https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&size=640x640&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U&signature=BhiRbuHKA-9TBW1kmeitFN1ObuA=

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Test-StaticUrl

If the URL is missing a required Static Maps parameter, such as the &size= parameter, the signStaticUrl function will return an error:
PS> $badUrl = "https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U"

PS> signStaticUrl $badUrl
signStaticUrl: Invalid Static URL:
signStaticUrl: >> https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9UsignStaticUrl: use: 'Test-StaticUrl <URL> -Verbose' for more information

As the error message notes, you can use Test-StaticUrl with the -Verbose parameter for more information:
PS> Test-StaticUrl $badUrl
VERBOSE: URL being tested:VERBOSE: https://maps.googleapis.com/maps/api/staticmap?center=Eiffel+Tower,Paris,France&zoom=14&scale=2&language=en-EN&key=AIzaSyAY4gcXw6gp_mlQ8qKisL5sE23LMC1MM9U
VERBOSE: URL must include a size parameter like "&size=640x400

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Using signStaticUrl and Test-StaticUrl in pipelines

The signStaticUrl function, its aliases, and the Test-StaticUrl function can be used in a PowerShell pipeline.

For example, if you have a list of Static Maps URLs in a text file: You can use:
Get-Content ./unsignedURLs.txt | Protect-StaticUrl
to sign each URL

Of course, you can redirect the signed URLs to a new file:
Get-Content ./unsignedURLs.txt | Protect-StaticUrl >signedURLs.txt

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Using signStaticUrl on objects in a pipeline

If you have a .CSV file containing lines of data about a number of locations (including a URL field in each row), you can use PowerShell's ForEach-Object, Import-CSV and Export-CSV commands with signStaticUrl to create a new .CSV file with signed URLs.

For example, if you have a locations.csv file with a list of retail locations, each with a store_number and a map_URL field, you can create locations_with_signature.csv using:

PS > Import-Csv ./locations.csv |
>> ForEach-Object {
>> $_.map_url = signStaticUrl $_.map_url; $_
>> } | Export-Csv ./locations_with_signature.csv

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