IdentityServer 3 returns invalid_client - oauth-2.0

Question

I am using IdentityServer3 with EF. I have API project and i want to authenticate its access using access token.
So based on sample i have configured client ( for API project) in identity server as below
Client Properties
Client Secret
(Note whatever the text i put as secret value, the admin UI automatically convert it)
Scope
Then using POSTMAN i am trying get access token, but i always get invalid_client error
I have also tried getting access token using C# code, but get the same error
static TokenResponse GetClientToken()
{
var client = new TokenClient(
"https://xxxxxxxx/connect/token",
"A0AD7FB8-2881-484F-xxxxxxxxxxxxxxxxxx",
"a84iThYxAA5eZpkIzt9xxxxxxxxxxxxxxxxxx");
return client.RequestClientCredentialsAsync("api").Result;
}
Update 1
Here is what i see in identity server's log
2018-12-21 19:29:59.284 +00:00 [Information] Start token request
2018-12-21 19:29:59.301 +00:00 [Debug] Start client validation
2018-12-21 19:29:59.302 +00:00 [Debug] Start parsing Basic Authentication secret
2018-12-21 19:29:59.302 +00:00 [Debug] Start parsing for secret in post body
2018-12-21 19:29:59.304 +00:00 [Debug] Parser found secret: "PostBodySecretParser"
2018-12-21 19:29:59.304 +00:00 [Information] Secret id found: "A0AD7FB8-2881-484F-ABE0-xxxxxxxx"
2018-12-21 19:29:59.943 +00:00 [Debug] Skipping secret: no description, secret is not of type SharedSecret.
2018-12-21 19:29:59.943 +00:00 [Debug] No matching hashed secret found.
2018-12-21 19:29:59.943 +00:00 [Information] Secret validators could not validate secret
2018-12-21 19:29:59.944 +00:00 [Information] Client validation failed.
2018-12-21 19:29:59.945 +00:00 [Information] End token request
2018-12-21 19:29:59.946 +00:00 [Information] Returning error: invalid_client
Update 2
(The the secret value is updated than what i have posted earlier)

Answer 1

Try secret type as SharedSecret instead of clientsecret. Identity Server 3 has the below secret types:
SharedSecret
X509Thumbprint
X509Name
X509CertificateBase64
Taken from Identity Server 3 source
Also, additionally you seem to be using hash value of the secret when sending auth requests a84iThYxAA5eZpkIzt9xxxxxxxxxxxxxxxxxx, however, you need to use the plain text value that you used to create the secret. (58b9....)

Answer 2

You could encounter invalid_client error in the different, quite curious case.
Updating IdentityServer3.EntityFramework (IS3.EF) to 2.5.1 seems to cause a change in both client secret and scope secret's default behaviour. Below this version even if you don't provide value for secret type in a database (leaving it as null) Identity Server will treat it as "SharedSecret". It sets it as such in class's constructor at the application level.
However, the newer IS.EF3 package contains an update of AutoMapper to 5.0 version. This update as a side effect seems to stop executing default constructors (with given configuration). This way setting client secret type in the database becomes de facto mandatory. Otherwise, you get invalid_client error, because secrets don't match their type.
It looks like authors intended to fix this behaviour change, but the branch hasn't been merged into master up till now:
ID3.EF - idea_for_setting_defaults_on_entities
Be advised, there already is Identity Server 4, so the merge may never occur.