Using the Cogos Analytics REST API from PowerShell

Using Cognos Analytics 11.2.4
Trying to write a PowerShell script to administer Cognos Analytics through the Cognos Analytics REST API. My first attempt is to create a new session (login). I'm getting nowhere so far.

Following documentation and help found at:
IBM Cognos Analytics REST API (and related)
https://MyServerName:9300/api/api-docs/
PowerShell Invoke-RestMethod
Unsupported Media Type when updating values using the TeamCity REST API

Whenever I try this I get an error:
Invoke-RestMethod : The remote server returned an error: (415) Unsupported Media Type.

The local API documentation on the server does not include 415 as a possible response. (...which wouldn't help anyway because the documentation doesn't include any likely causation with the error responses that are in the docs.)

How can I get past this? I could really use a nudge in the right direction.

Here is the code I have tried. Previous attempts are included and commented out.

#  docs at
#  http://<cognos_analytics_server>:<port>/api/api-docs

$serverName = "<cognos_analytics_server>"
$port = "<port>"
$userNamespace = "<external_directory_namespace>"
$userName = Read-Host "User Name:  "

$pwd = Read-Host "Password" -AsSecureString
$bstr = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($pwd)
$userPassword = [System.Runtime.InteropServices.Marshal]::PtrToStringAuto($bstr)
# then free up the unmanged memory afterwards
[Runtime.InteropServices.Marshal]::ZeroFreeBSTR($bstr)

#  Attempt 1
#$p = @()
#$p += @{
#      name = "CAMNamespace"
#      value = $userNamespace
#    }
#$p += @{
#      name = "CAMUsername"
#      value = $userName
#    }
#$p += @{
#      name = "CAMPassword"
#      value = $userPassword
#    }
#
#$body = @{
#  parameters = $p
#}

#  Attempt 2
#$body = '{
#  "parameters": [
#    {
#      "name": "CAMNamespace",
#      "value": "' + $userNamespace + '"
#    },
#    {
#      "name": "CAMUsername",
#      "value": "' + $userName + '"
#    },
#    {
#      "name": "CAMPassword",
#      "value": "' + $userPassword + '"
#    }
#  ]
#}'

#  Attempt 3
#$body = '{"parameters": [{"name": "CAMNamespace","value": "' + $userNamespace + '"},{"name": "CAMUsername","value": "' + $userName + '"},{"name": "CAMPassword","value": "' + $userPassword + '"}]}'

#  Attempt 4
#$body = "{`"parameters`": [{`"name`": `"CAMNamespace`",`"value`": `"$userNamespace`"},{`"name`": `"CAMUsername`",`"value`": `"$userName`"},{`"name`": `"CAMPassword`",`"value`": `"$userPassword`"}]}"

#  Attempt 5
$body = "{
  `"parameters`": [
    {
      `"name`": `"CAMNamespace`",
      `"value`": `"$userNamespace`"
    },
    {
      `"name`": `"CAMUsername`",
      `"value`": `"$userName`"
    },
    {
      `"name`": `"CAMPassword`",
      `"value`": `"$userPassword`"
    }
  ]
}"


$uri = "$protocol`://$serverName`:$port/api/v1/session"

#  Attempt 1
#Invoke-RestMethod -Uri $uri -Method Put -Body $body

#  Further attempts
Invoke-RestMethod -contentType "text/plain" -Uri $uri -Method Put -Body $body

The Swagger documentation at https://www.ibm.com/docs/swagger/?configuration=SSEP7J_12.0.0/com.ibm.swg.ba.cognos.ca_api.doc/swagger_ca.json#/session/create_update_session gives a little bit more of a clue about how to make a correct request:

If you change your code to:

Invoke-RestMethod -ContentType "application/json" -Uri $uri -Method Put -Body $body

it might get you past the "Unsupported Media" error.

@DanielWagemann's link to the documentation at https://developer.ibm.com/apis/catalog/cognosanalytics--cognos-analytics-rest-api/api/API--cognosanalytics--cognos-analytics#create_update_session also includes a curl example that you can use to model your Invoke-RestMethod calls:

curl --request PUT \
  --url REPLACE_ENDPOINT_VARIABLE/api/v1/session \
  --header 'IBM-BA-Authorization: REPLACE_THIS_VALUE' \
  --header 'accept: application/json' \
  --header 'content-type: application/json' \
  --data REPLACE_REQUEST_BODY

See --header 'content-type: application/json' above which basically suggests using -ContentType "application/json" for Invoke-RestMethod as well...