Functions/Get-JsonWebTokenHeader.ps1
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function Get-JsonWebTokenHeader { <# .SYNOPSIS Gets the JSON Web Token header from the passed JWT. .DESCRIPTION Deserializes a JSON Web Token header to a System.Collections.HashTable by default. Optionally a string (base 64 encoded or JSON) is returned depending on parameters chosen. .PARAMETER JsonWebToken Specifies the The JSON Web Token to get the header from. .PARAMETER AsEncodedString Returns the header as a base 64 URL encoded string. .PARAMETER AsJson Returns the header as a JSON string. .EXAMPLE $jwt = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.VG6H-orYnMLknmJajHx1HW9SftqCWeqE3TQ1UArx3Mk" $jwt | Get-JsonWebTokenHeader Returns the header from the passed JWT as a Hashtable. .EXAMPLE $jwt = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.VG6H-orYnMLknmJajHx1HW9SftqCWeqE3TQ1UArx3Mk" Get-JsonWebTokenHeader -JsonWebToken $jwt -AsEncodedString Returns the encoded header from the passed JWT. .EXAMPLE $jwt = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.VG6H-orYnMLknmJajHx1HW9SftqCWeqE3TQ1UArx3Mk" Get-JsonWebTokenHeader -JsonWebToken $jwt -AsJson Returns the decoded header from the passed JWT. .INPUTS System.String A String is received by the JsonWebToken parameter. .OUTPUTS System.Collections.Hashtable or System.String .LINK New-JsonWebToken Test-JsonWebToken Get-JsonWebTokenPayload Get-JsonWebTokenSignature #> [CmdletBinding(DefaultParameterSetName = "Default")] [Alias('gjwth')] [OutputType([System.Collections.Hashtable])] [OutputType([System.String], ParameterSetName = "Base64")] [OutputType([System.String], ParameterSetName = "JSON")] Param ( [Parameter(Mandatory = $true, ValueFromPipeline = $true, Position = 0)] [ValidateLength(16, 8192)][Alias("JWT", "Token")][String]$JsonWebToken, [Parameter(ParameterSetName = "Base64", Mandatory = $true, ValueFromPipeline = $false, ValueFromPipelineByPropertyName = $false, Position = 1)][Alias("AsIs")][switch]$AsEncodedString, [Parameter(ParameterSetName = "JSON", Mandatory = $true, ValueFromPipeline = $false, ValueFromPipelineByPropertyName = $false, Position = 1)][Alias("json")][switch]$AsJson ) BEGIN { $decodeExceptionMessage = "Unable to decode JWT." $ArgumentException = New-Object -TypeName ArgumentException -ArgumentList $decodeExceptionMessage } PROCESS { [bool]$isValidJwt = Test-JwtStructure -JsonWebToken $JsonWebToken if (-not($isValidJwt)) { Write-Error -Exception $ArgumentException -Category InvalidData -ErrorAction Stop } $jwtHeader = $JsonWebToken.Split(".")[0] if ($PSBoundParameters.ContainsKey("AsEncodedString")) { return $jwtHeader } elseif ($PSBoundParameters.ContainsKey("AsJson")) { return $jwtHeader | ConvertFrom-Base64UrlEncodedString } else { [System.Collections.Hashtable]$jwtHeaderTable = $jwtHeader | ConvertFrom-Base64UrlEncodedString | ConvertFrom-Json | Convert-PSObjectToHashTable return $jwtHeaderTable } } } |