Question: how to remove an application logo.
Solution: previous solution from this answer, https://stackoverflow.com/a/57168008/1992004, is no longer working.
Google changed the format of "iconUrl" to "icon", and uses now the Base64-encoded data stream, like "icon":"iVBORw0KGgoAAAAN..., instead of the image URL, previously written as "iconUrl":"https://...".
I've tried "icon":"" and many Base64-encoded values like "icon":"IA", "icon":"Lw", and some of other - no success. I get console messages like
for "icon":""
{
"error": {
"code": 400,
"message": "The request failed because one of the field of the resource is invalid.",
"status": "INVALID_ARGUMENT",
"details": [
{
"@type": "type.googleapis.com/google.rpc.PreconditionFailure",
"violations": [
{
"type": "client_auth_config",
"subject": "?error_code=9&error_field_name=UpdateIconRequest.icon&error_field_value=%3CByteString@3eeee81e+size%3D0+contents%3D%22%22%3E"
}
]
}
]
}
}
or
{
"error": {
"code": 400,
"message": "Request contains an invalid argument.",
"status": "INVALID_ARGUMENT",
"details": [
{
"@type": "type.googleapis.com/google.identity.clientauthconfig.v1.ClientAuthConfigError",
"code": "ICON_STORAGE_FAILURE"
},
{
"@type": "type.googleapis.com/google.identity.clientauthconfig.v1.IconStorageError",
"reason": "INVALID_IMAGE"
}
]
}
}
or
{
"error": {
"code": 400,
"message": "Invalid value at 'icon' (TYPE_BYTES), Base64 decoding failed for \" \"",
"status": "INVALID_ARGUMENT",
"details": [
{
"@type": "type.googleapis.com/google.rpc.BadRequest",
"fieldViolations": [
{
"field": "icon",
"description": "Invalid value at 'icon' (TYPE_BYTES), Base64 decoding failed for \" \""
}
]
}
]
}
}
Does somebody know, what should be inserted here to remove the logo image from the app?
Unfortunately, there is no way for this to be done.
Once an OAuth Application Logo has been uploaded there isn't a supported way of removing it - in the question that you linked the way that this was done is a bit hacky, inspecting the network requests and building a new request from the previous JSON object sent via the UI really shows this.
As the icon URL has changed to need a Base-64 encoded value this has been deprecated. Whether this was intentional by Google or not is hard to say, but now an empty value will always return INVALID_ARGUMENT. Any data in the value for icon will also just replace the image data and so this isn't a viable workaround, as as far as the validation process goes, image data exists and so will need to be verified.
If it's not too much of a arduous process, the only workaround here is to create a new GCP project with a new OAuth consent screen without uploading an image. Of course, you will need to reactivate all the relevant APIs and link the relevant scripts and projects to the new set-up.
You can however let Google know that this is a feature that is important and that you would like to request they implement it. Google's Issue Tracker is a place for developers to report issues and make feature requests for their development services. I would suggest using the feature request template for G Suite Add-ons as this is a component for which GCP Projects could be used.
Update: The feature request for this is viewable here, to increase visibility on this, hit the ☆ at the top of the page.